diff --git a/changes/4538-sisp.md b/changes/4538-sisp.md
new file mode 100644
index 0000000000..afb3312ba5
--- /dev/null
+++ b/changes/4538-sisp.md
@@ -0,0 +1 @@
+Fix field regex with `StrictStr` type annotation.
diff --git a/pydantic/types.py b/pydantic/types.py
index f98dba3de4..eaf679d48e 100644
--- a/pydantic/types.py
+++ b/pydantic/types.py
@@ -403,7 +403,7 @@ class ConstrainedStr(str):
     min_length: OptionalInt = None
     max_length: OptionalInt = None
     curtail_length: OptionalInt = None
-    regex: Optional[Pattern[str]] = None
+    regex: Optional[Union[str, Pattern[str]]] = None
     strict = False
 
     @classmethod
@@ -412,7 +412,7 @@ def __modify_schema__(cls, field_schema: Dict[str, Any]) -> None:
             field_schema,
             minLength=cls.min_length,
             maxLength=cls.max_length,
-            pattern=cls.regex and cls.regex.pattern,
+            pattern=cls.regex and cls._get_pattern(cls.regex),
         )
 
     @classmethod
@@ -430,11 +430,15 @@ def validate(cls, value: Union[str]) -> Union[str]:
             value = value[: cls.curtail_length]
 
         if cls.regex:
-            if not cls.regex.match(value):
-                raise errors.StrRegexError(pattern=cls.regex.pattern)
+            if not re.match(cls.regex, value):
+                raise errors.StrRegexError(pattern=cls._get_pattern(cls.regex))
 
         return value
 
+    @staticmethod
+    def _get_pattern(regex: Union[str, Pattern[str]]) -> str:
+        return regex if isinstance(regex, str) else regex.pattern
+
 
 def constr(
     *,
diff --git a/tests/test_types.py b/tests/test_types.py
index af4a91ef1d..785e335b91 100644
--- a/tests/test_types.py
+++ b/tests/test_types.py
@@ -1759,6 +1759,45 @@ class Model(BaseModel):
         Model(u='1234567')
 
 
+def test_strict_str_regex():
+    class Model(BaseModel):
+        u: StrictStr = Field(..., regex=r'^[0-9]+$')
+
+    assert Model(u='123').u == '123'
+
+    with pytest.raises(ValidationError, match='str type expected'):
+        Model(u=123)
+
+    with pytest.raises(ValidationError) as exc_info:
+        Model(u='abc')
+    assert exc_info.value.errors() == [
+        {
+            'loc': ('u',),
+            'msg': 'string does not match regex "^[0-9]+$"',
+            'type': 'value_error.str.regex',
+            'ctx': {'pattern': '^[0-9]+$'},
+        }
+    ]
+
+
+def test_string_regex():
+    class Model(BaseModel):
+        u: str = Field(..., regex=r'^[0-9]+$')
+
+    assert Model(u='123').u == '123'
+
+    with pytest.raises(ValidationError) as exc_info:
+        Model(u='abc')
+    assert exc_info.value.errors() == [
+        {
+            'loc': ('u',),
+            'msg': 'string does not match regex "^[0-9]+$"',
+            'type': 'value_error.str.regex',
+            'ctx': {'pattern': '^[0-9]+$'},
+        }
+    ]
+
+
 def test_strict_bool():
     class Model(BaseModel):
         v: StrictBool