diff --git a/relay/channel/gemini/adaptor.go b/relay/channel/gemini/adaptor.go
index d71c369b..021ed062 100644
--- a/relay/channel/gemini/adaptor.go
+++ b/relay/channel/gemini/adaptor.go
@@ -86,12 +86,25 @@ func getImageSizeMapping() QualityMapping {
 
 func getSizeMappings() map[string]SizeMapping {
 	return map[string]SizeMapping{
+		// Gemini 2.5 Flash Image - default 1K resolutions
+		"1024x1024": {AspectRatio: "1:1", ImageSize: ""},
+		"832x1248":  {AspectRatio: "2:3", ImageSize: ""},
+		"1248x832":  {AspectRatio: "3:2", ImageSize: ""},
+		"864x1184":  {AspectRatio: "3:4", ImageSize: ""},
+		"1184x864":  {AspectRatio: "4:3", ImageSize: ""},
+		"896x1152":  {AspectRatio: "4:5", ImageSize: ""},
+		"1152x896":  {AspectRatio: "5:4", ImageSize: ""},
+		"768x1344":  {AspectRatio: "9:16", ImageSize: ""},
+		"1344x768":  {AspectRatio: "16:9", ImageSize: ""},
+		"1536x672":  {AspectRatio: "21:9", ImageSize: ""},
+
+		// Gemini 3 Pro Image Preview resolutions
 		"1536x1024": {AspectRatio: "3:2", ImageSize: ""},
 		"1024x1536": {AspectRatio: "2:3", ImageSize: ""},
 		"1024x1792": {AspectRatio: "9:16", ImageSize: ""},
 		"1792x1024": {AspectRatio: "16:9", ImageSize: ""},
-		"2048x2048": {AspectRatio: "", ImageSize: "2K"},
-		"4096x4096": {AspectRatio: "", ImageSize: "4K"},
+		"2048x2048": {AspectRatio: "1:1", ImageSize: "2K"},
+		"4096x4096": {AspectRatio: "1:1", ImageSize: "4K"},
 	}
 }
 
@@ -140,13 +153,13 @@ func (a *Adaptor) ConvertImageRequest(c *gin.Context, info *relaycommon.RelayInf
 
 		config := processSizeParameters(strings.TrimSpace(request.Size), request.Quality)
 		googleGenerationConfig := map[string]interface{}{
-			"response_modalities": []string{"TEXT", "IMAGE"},
-			"image_config":        config,
+			"responseModalities": []string{"TEXT", "IMAGE"},
+			"imageConfig":        config,
 		}
 
 		extraBody := map[string]interface{}{
 			"google": map[string]interface{}{
-				"generation_config": googleGenerationConfig,
+				"generationConfig": googleGenerationConfig,
 			},
 		}
 		chatRequest.ExtraBody, _ = json.Marshal(extraBody)
diff --git a/relay/channel/gemini/relay-gemini.go b/relay/channel/gemini/relay-gemini.go
index 0628b105..7776847b 100644
--- a/relay/channel/gemini/relay-gemini.go
+++ b/relay/channel/gemini/relay-gemini.go
@@ -239,6 +239,16 @@ func CovertOpenAI2Gemini(c *gin.Context, textRequest dto.GeneralOpenAIRequest, i
 						}
 					}
 				}
+
+				if generationConfig, ok := googleBody["generationConfig"].(map[string]any); ok {
+					generationConfigBytes, err := json.Marshal(generationConfig)
+					if err != nil {
+						return nil, fmt.Errorf("failed to marshal generationConfig: %w", err)
+					}
+					if err := json.Unmarshal(generationConfigBytes, &geminiRequest.GenerationConfig); err != nil {
+						return nil, fmt.Errorf("failed to unmarshal generationConfig: %w", err)
+					}
+				}
 			}
 		}
 	}