diff --git a/modules/openapi-generator/src/main/resources/dart/api.mustache b/modules/openapi-generator/src/main/resources/dart/api.mustache
index 6ed091fc7ee..373ce2508b3 100644
--- a/modules/openapi-generator/src/main/resources/dart/api.mustache
+++ b/modules/openapi-generator/src/main/resources/dart/api.mustache
@@ -89,22 +89,22 @@ class {{classname}} {
                                              authNames);
 
     if(response.statusCode >= 400) {
-      throw new ApiException(response.statusCode, response.body);
+      throw new ApiException(response.statusCode, _decodeBodyBytes(response));
     } else if(response.body != null) {
       {{#isListContainer}}
         {{#returnType}}
-      return (apiClient.deserialize(response.body, '{{{returnType}}}') as List).map((item) => item as {{returnBaseType}}).toList();
+      return (apiClient.deserialize(_decodeBodyBytes(response), '{{{returnType}}}') as List).map((item) => item as {{returnBaseType}}).toList();
         {{/returnType}}
       {{/isListContainer}}
       {{^isListContainer}}
         {{#isMapContainer}}
           {{#returnType}}
-      return new {{{returnType}}}.from(apiClient.deserialize(response.body, '{{{returnType}}}'));
+      return new {{{returnType}}}.from(apiClient.deserialize(_decodeBodyBytes(response), '{{{returnType}}}'));
           {{/returnType}};
         {{/isMapContainer}}
         {{^isMapContainer}}
           {{#returnType}}
-      return apiClient.deserialize(response.body, '{{{returnType}}}') as {{{returnType}}};
+      return apiClient.deserialize(_decodeBodyBytes(response), '{{{returnType}}}') as {{{returnType}}};
           {{/returnType}}
         {{/isMapContainer}}
       {{/isListContainer}}
diff --git a/modules/openapi-generator/src/main/resources/dart/api_helper.mustache b/modules/openapi-generator/src/main/resources/dart/api_helper.mustache
index 3929fa2b762..73b2585b1b4 100644
--- a/modules/openapi-generator/src/main/resources/dart/api_helper.mustache
+++ b/modules/openapi-generator/src/main/resources/dart/api_helper.mustache
@@ -50,3 +50,15 @@ String parameterToString(dynamic value) {
     return value.toString();
   }
 }
+
+/// Returns the decoded body by utf-8 if application/json with the given headers.
+/// Else, returns the decoded body by default algorithm of dart:http.
+/// Because avoid to text garbling when header only contains "application/json" without "; charset=utf-8".
+String _decodeBodyBytes(Response response) {
+  var contentType = response.headers['content-type'];
+  if (contentType != null && contentType.contains("application/json")) {
+    return utf8.decode(response.bodyBytes);
+  } else {
+    return response.body;
+  }
+}
diff --git a/modules/openapi-generator/src/main/resources/dart2/api.mustache b/modules/openapi-generator/src/main/resources/dart2/api.mustache
index 76797fa2ddc..3a29f01f827 100644
--- a/modules/openapi-generator/src/main/resources/dart2/api.mustache
+++ b/modules/openapi-generator/src/main/resources/dart2/api.mustache
@@ -89,22 +89,22 @@ class {{classname}} {
                                              authNames);
 
     if(response.statusCode >= 400) {
-      throw new ApiException(response.statusCode, response.body);
+      throw new ApiException(response.statusCode, _decodeBodyBytes(response));
     } else if(response.body != null) {
       {{#isListContainer}}
         {{#returnType}}
-      return (apiClient.deserialize(response.body, '{{{returnType}}}') as List).map((item) => item as {{returnBaseType}}).toList();
+      return (apiClient.deserialize(_decodeBodyBytes(response), '{{{returnType}}}') as List).map((item) => item as {{returnBaseType}}).toList();
         {{/returnType}}
       {{/isListContainer}}
       {{^isListContainer}}
         {{#isMapContainer}}
           {{#returnType}}
-      return new {{{returnType}}}.from(apiClient.deserialize(response.body, '{{{returnType}}}'));
+      return new {{{returnType}}}.from(apiClient.deserialize(_decodeBodyBytes(response), '{{{returnType}}}'));
           {{/returnType}};
         {{/isMapContainer}}
         {{^isMapContainer}}
           {{#returnType}}
-      return apiClient.deserialize(response.body, '{{{returnType}}}') as {{{returnType}}};
+      return apiClient.deserialize(_decodeBodyBytes(response), '{{{returnType}}}') as {{{returnType}}};
           {{/returnType}}
         {{/isMapContainer}}
       {{/isListContainer}}
diff --git a/modules/openapi-generator/src/main/resources/dart2/api_helper.mustache b/modules/openapi-generator/src/main/resources/dart2/api_helper.mustache
index 1e554bede4b..7027f30a5b6 100644
--- a/modules/openapi-generator/src/main/resources/dart2/api_helper.mustache
+++ b/modules/openapi-generator/src/main/resources/dart2/api_helper.mustache
@@ -50,3 +50,15 @@ String parameterToString(dynamic value) {
     return value.toString();
   }
 }
+
+/// Returns the decoded body by utf-8 if application/json with the given headers.
+/// Else, returns the decoded body by default algorithm of dart:http.
+/// Because avoid to text garbling when header only contains "application/json" without "; charset=utf-8".
+String _decodeBodyBytes(Response response) {
+  var contentType = response.headers['content-type'];
+  if (contentType != null && contentType.contains("application/json")) {
+    return utf8.decode(response.bodyBytes);
+  } else {
+    return response.body;
+  }
+}