diff --git a/slack_bolt/app/async_app.py b/slack_bolt/app/async_app.py
index 62adbc40e..86211f175 100644
--- a/slack_bolt/app/async_app.py
+++ b/slack_bolt/app/async_app.py
@@ -34,6 +34,8 @@
     error_listener_function_must_be_coro_func,
     error_client_invalid_type_async,
     error_authorize_conflicts,
+    error_oauth_settings_invalid_type_async,
+    error_oauth_flow_invalid_type_async,
 )
 from slack_bolt.lazy_listener.asyncio_runner import AsyncioLazyListenerRunner
 from slack_bolt.listener.async_listener import AsyncListener, AsyncCustomListener
@@ -167,6 +169,9 @@ def __init__(
             oauth_settings = AsyncOAuthSettings()
 
         if oauth_flow:
+            if not isinstance(oauth_flow, AsyncOAuthFlow):
+                raise BoltError(error_oauth_flow_invalid_type_async())
+
             self._async_oauth_flow = oauth_flow
             installation_store = select_consistent_installation_store(
                 client_id=self._async_oauth_flow.client_id,
@@ -182,6 +187,9 @@ def __init__(
             if self._async_authorize is None:
                 self._async_authorize = self._async_oauth_flow.settings.authorize
         elif oauth_settings is not None:
+            if not isinstance(oauth_settings, AsyncOAuthSettings):
+                raise BoltError(error_oauth_settings_invalid_type_async())
+
             installation_store = select_consistent_installation_store(
                 client_id=oauth_settings.client_id,
                 app_store=self._async_installation_store,
diff --git a/slack_bolt/logger/messages.py b/slack_bolt/logger/messages.py
index 29ee7bfe0..291ddf1d3 100644
--- a/slack_bolt/logger/messages.py
+++ b/slack_bolt/logger/messages.py
@@ -26,6 +26,14 @@ def error_client_invalid_type_async() -> str:
     return "`client` must be a slack_sdk.web.async_client.AsyncWebClient"
 
 
+def error_oauth_flow_invalid_type_async() -> str:
+    return "`oauth_flow` must be a slack_bolt.oauth.async_oauth_flow.AsyncOAuthFlow"
+
+
+def error_oauth_settings_invalid_type_async() -> str:
+    return "`oauth_settings` must be a slack_bolt.oauth.async_oauth_settings.AsyncOAuthSettings"
+
+
 def error_auth_test_failure(error_response: SlackResponse) -> str:
     return f"`token` is invalid (auth.test result: {error_response})"
 
diff --git a/slack_bolt/oauth/async_oauth_flow.py b/slack_bolt/oauth/async_oauth_flow.py
index 1157dd632..073a622e3 100644
--- a/slack_bolt/oauth/async_oauth_flow.py
+++ b/slack_bolt/oauth/async_oauth_flow.py
@@ -4,6 +4,7 @@
 from typing import Optional, Dict, Callable, Awaitable, Sequence
 
 from slack_bolt.error import BoltError
+from slack_bolt.logger.messages import error_oauth_settings_invalid_type_async
 from slack_bolt.oauth.async_callback_options import (
     AsyncCallbackOptions,
     DefaultAsyncCallbackOptions,
@@ -62,7 +63,11 @@ def __init__(
         """
         self._async_client = client
         self._logger = logger
+
+        if not isinstance(settings, AsyncOAuthSettings):
+            raise BoltError(error_oauth_settings_invalid_type_async())
         self.settings = settings
+
         self.settings.logger = self._logger
 
         self.client_id = self.settings.client_id
diff --git a/slack_bolt/oauth/async_oauth_settings.py b/slack_bolt/oauth/async_oauth_settings.py
index 6b2431ef7..f09df9a0d 100644
--- a/slack_bolt/oauth/async_oauth_settings.py
+++ b/slack_bolt/oauth/async_oauth_settings.py
@@ -1,7 +1,7 @@
 import logging
 import os
 from logging import Logger
-from typing import Optional, Sequence
+from typing import Optional, Sequence, Union
 
 from slack_sdk.oauth import (
     OAuthStateUtils,
@@ -57,8 +57,8 @@ def __init__(
         # OAuth flow parameters/credentials
         client_id: Optional[str] = None,  # required
         client_secret: Optional[str] = None,  # required
-        scopes: Optional[Sequence[str]] = None,
-        user_scopes: Optional[Sequence[str]] = None,
+        scopes: Optional[Union[Sequence[str], str]] = None,
+        user_scopes: Optional[Union[Sequence[str], str]] = None,
         redirect_uri: Optional[str] = None,
         # Handler configuration
         install_path: str = "/slack/install",
@@ -104,9 +104,13 @@ def __init__(
             raise BoltError("Both client_id and client_secret are required")
 
         self.scopes = scopes or os.environ.get("SLACK_SCOPES", "").split(",")
+        if isinstance(self.scopes, str):
+            self.scopes = self.scopes.split(",")
         self.user_scopes = user_scopes or os.environ.get("SLACK_USER_SCOPES", "").split(
             ","
         )
+        if isinstance(self.user_scopes, str):
+            self.user_scopes = self.user_scopes.split(",")
         self.redirect_uri = redirect_uri or os.environ.get("SLACK_REDIRECT_URI")
         # Handler configuration
         self.install_path = install_path or os.environ.get(
diff --git a/slack_bolt/oauth/oauth_settings.py b/slack_bolt/oauth/oauth_settings.py
index 3dd49e1ef..1462925c2 100644
--- a/slack_bolt/oauth/oauth_settings.py
+++ b/slack_bolt/oauth/oauth_settings.py
@@ -1,7 +1,7 @@
 import logging
 import os
 from logging import Logger
-from typing import Optional, Sequence
+from typing import Optional, Sequence, Union
 
 from slack_sdk.oauth import (
     OAuthStateStore,
@@ -52,8 +52,8 @@ def __init__(
         # OAuth flow parameters/credentials
         client_id: Optional[str] = None,  # required
         client_secret: Optional[str] = None,  # required
-        scopes: Optional[Sequence[str]] = None,
-        user_scopes: Optional[Sequence[str]] = None,
+        scopes: Optional[Union[Sequence[str], str]] = None,
+        user_scopes: Optional[Union[Sequence[str], str]] = None,
         redirect_uri: Optional[str] = None,
         # Handler configuration
         install_path: str = "/slack/install",
@@ -98,9 +98,13 @@ def __init__(
             raise BoltError("Both client_id and client_secret are required")
 
         self.scopes = scopes or os.environ.get("SLACK_SCOPES", "").split(",")
+        if isinstance(self.scopes, str):
+            self.scopes = self.scopes.split(",")
         self.user_scopes = user_scopes or os.environ.get("SLACK_USER_SCOPES", "").split(
             ","
         )
+        if isinstance(self.user_scopes, str):
+            self.user_scopes = self.user_scopes.split(",")
         self.redirect_uri = redirect_uri or os.environ.get("SLACK_REDIRECT_URI")
         # Handler configuration
         self.install_path = install_path or os.environ.get(
diff --git a/tests/slack_bolt/oauth/test_oauth_flow.py b/tests/slack_bolt/oauth/test_oauth_flow.py
index 5d390f7bf..a2797e5e0 100644
--- a/tests/slack_bolt/oauth/test_oauth_flow.py
+++ b/tests/slack_bolt/oauth/test_oauth_flow.py
@@ -46,6 +46,7 @@ def test_handle_installation(self):
                 client_id="111.222",
                 client_secret="xxx",
                 scopes=["chat:write", "commands"],
+                user_scopes=["search:read"],
                 installation_store=FileInstallationStore(),
                 state_store=FileOAuthStateStore(expiration_seconds=120),
             )
@@ -54,9 +55,19 @@ def test_handle_installation(self):
         resp = oauth_flow.handle_installation(req)
         assert resp.status == 200
         assert resp.headers.get("content-type") == ["text/html; charset=utf-8"]
-        assert resp.headers.get("content-length") == ["565"]
+        assert resp.headers.get("content-length") == ["576"]
         assert "https://slack.com/oauth/v2/authorize?state=" in resp.body
 
+    def test_scopes_as_str(self):
+        settings = OAuthSettings(
+            client_id="111.222",
+            client_secret="xxx",
+            scopes="chat:write,commands",
+            user_scopes="search:read",
+        )
+        assert settings.scopes == ["chat:write", "commands"]
+        assert settings.user_scopes == ["search:read"]
+
     def test_handle_callback(self):
         oauth_flow = OAuthFlow(
             client=WebClient(base_url=self.mock_api_server_base_url),
diff --git a/tests/slack_bolt_async/oauth/test_async_oauth_flow.py b/tests/slack_bolt_async/oauth/test_async_oauth_flow.py
index 85968ed0c..44f4e5ea7 100644
--- a/tests/slack_bolt_async/oauth/test_async_oauth_flow.py
+++ b/tests/slack_bolt_async/oauth/test_async_oauth_flow.py
@@ -11,6 +11,7 @@
 
 from slack_bolt import BoltResponse
 from slack_bolt.app.async_app import AsyncApp
+from slack_bolt.error import BoltError
 from slack_bolt.oauth.async_callback_options import (
     AsyncFailureArgs,
     AsyncSuccessArgs,
@@ -18,6 +19,7 @@
 )
 from slack_bolt.oauth.async_oauth_flow import AsyncOAuthFlow
 from slack_bolt.oauth.async_oauth_settings import AsyncOAuthSettings
+from slack_bolt.oauth.oauth_settings import OAuthSettings
 from slack_bolt.request.async_request import AsyncBoltRequest
 from tests.mock_web_api_server import (
     cleanup_mock_web_api_server,
@@ -46,6 +48,7 @@ async def test_instantiation(self):
                 client_id="111.222",
                 client_secret="xxx",
                 scopes=["chat:write", "commands"],
+                user_scopes=["search:read"],
                 installation_store=FileInstallationStore(),
                 state_store=FileOAuthStateStore(expiration_seconds=120),
             )
@@ -54,6 +57,40 @@ async def test_instantiation(self):
         assert oauth_flow.logger is not None
         assert oauth_flow.client is not None
 
+    @pytest.mark.asyncio
+    async def test_scopes_as_str(self):
+        settings = AsyncOAuthSettings(
+            client_id="111.222",
+            client_secret="xxx",
+            scopes="chat:write,commands",
+            user_scopes="search:read",
+        )
+        assert settings.scopes == ["chat:write", "commands"]
+        assert settings.user_scopes == ["search:read"]
+
+    @pytest.mark.asyncio
+    async def test_instantiation_non_async_settings(self):
+        with pytest.raises(BoltError):
+            AsyncOAuthFlow(
+                settings=OAuthSettings(
+                    client_id="111.222",
+                    client_secret="xxx",
+                    scopes="chat:write,commands",
+                )
+            )
+
+    @pytest.mark.asyncio
+    async def test_instantiation_non_async_settings_to_app(self):
+        with pytest.raises(BoltError):
+            AsyncApp(
+                signing_secret="xxx",
+                oauth_settings=OAuthSettings(
+                    client_id="111.222",
+                    client_secret="xxx",
+                    scopes="chat:write,commands",
+                ),
+            )
+
     @pytest.mark.asyncio
     async def test_handle_installation(self):
         oauth_flow = AsyncOAuthFlow(