diff --git a/weed/s3api/policy_conversion.go b/weed/s3api/policy_conversion.go
new file mode 100644
index 000000000..2f9d5be0a
--- /dev/null
+++ b/weed/s3api/policy_conversion.go
@@ -0,0 +1,172 @@
+package s3api
+
+import (
+	"github.com/seaweedfs/seaweedfs/weed/iam/policy"
+	"github.com/seaweedfs/seaweedfs/weed/s3api/policy_engine"
+)
+
+// ConvertPolicyDocumentToPolicyEngine converts a policy.PolicyDocument to policy_engine.PolicyDocument
+// This function provides efficient type conversion without JSON marshaling overhead.
+// It handles the differences between the two types:
+// - Converts []string fields to StringOrStringSlice
+// - Maps Condition types
+// - Handles optional fields (Id, NotPrincipal, NotAction, NotResource are ignored in policy_engine)
+func ConvertPolicyDocumentToPolicyEngine(src *policy.PolicyDocument) *policy_engine.PolicyDocument {
+	if src == nil {
+		return nil
+	}
+
+	dest := &policy_engine.PolicyDocument{
+		Version:   src.Version,
+		Statement: make([]policy_engine.PolicyStatement, len(src.Statement)),
+	}
+
+	for i, srcStmt := range src.Statement {
+		dest.Statement[i] = convertStatement(&srcStmt)
+	}
+
+	return dest
+}
+
+// convertStatement converts a policy.Statement to policy_engine.PolicyStatement
+func convertStatement(src *policy.Statement) policy_engine.PolicyStatement {
+	stmt := policy_engine.PolicyStatement{
+		Sid:    src.Sid,
+		Effect: policy_engine.PolicyEffect(src.Effect),
+	}
+
+	// Convert Action ([]string to StringOrStringSlice)
+	if len(src.Action) > 0 {
+		stmt.Action = policy_engine.NewStringOrStringSlice(src.Action...)
+	}
+
+	// Convert Resource ([]string to StringOrStringSlice)
+	if len(src.Resource) > 0 {
+		stmt.Resource = policy_engine.NewStringOrStringSlice(src.Resource...)
+	}
+
+	// Convert Principal (interface{} to *StringOrStringSlice)
+	if src.Principal != nil {
+		stmt.Principal = convertPrincipal(src.Principal)
+	}
+
+	// Convert Condition (map[string]map[string]interface{} to PolicyConditions)
+	if len(src.Condition) > 0 {
+		stmt.Condition = convertCondition(src.Condition)
+	}
+
+	return stmt
+}
+
+// convertPrincipal converts a Principal field to *StringOrStringSlice
+func convertPrincipal(principal interface{}) *policy_engine.StringOrStringSlice {
+	if principal == nil {
+		return nil
+	}
+
+	switch p := principal.(type) {
+	case string:
+		result := policy_engine.NewStringOrStringSlice(p)
+		return &result
+	case []string:
+		result := policy_engine.NewStringOrStringSlice(p...)
+		return &result
+	case []interface{}:
+		// Convert []interface{} to []string
+		strs := make([]string, 0, len(p))
+		for _, v := range p {
+			if str, ok := v.(string); ok {
+				strs = append(strs, str)
+			}
+		}
+		if len(strs) > 0 {
+			result := policy_engine.NewStringOrStringSlice(strs...)
+			return &result
+		}
+	case map[string]interface{}:
+		// Handle AWS-style principal with service/user keys
+		// Example: {"AWS": "arn:aws:iam::123456789012:user/Alice"}
+		strs := make([]string, 0)
+		for _, v := range p {
+			switch val := v.(type) {
+			case string:
+				strs = append(strs, val)
+			case []string:
+				strs = append(strs, val...)
+			case []interface{}:
+				for _, item := range val {
+					if str, ok := item.(string); ok {
+						strs = append(strs, str)
+					}
+				}
+			}
+		}
+		if len(strs) > 0 {
+			result := policy_engine.NewStringOrStringSlice(strs...)
+			return &result
+		}
+	}
+
+	return nil
+}
+
+// convertCondition converts policy conditions to PolicyConditions
+func convertCondition(src map[string]map[string]interface{}) policy_engine.PolicyConditions {
+	if len(src) == 0 {
+		return nil
+	}
+
+	dest := make(policy_engine.PolicyConditions)
+	for condType, condBlock := range src {
+		destBlock := make(map[string]policy_engine.StringOrStringSlice)
+		for key, value := range condBlock {
+			destBlock[key] = convertConditionValue(value)
+		}
+		dest[condType] = destBlock
+	}
+
+	return dest
+}
+
+// convertConditionValue converts a condition value to StringOrStringSlice
+func convertConditionValue(value interface{}) policy_engine.StringOrStringSlice {
+	switch v := value.(type) {
+	case string:
+		return policy_engine.NewStringOrStringSlice(v)
+	case []string:
+		return policy_engine.NewStringOrStringSlice(v...)
+	case []interface{}:
+		strs := make([]string, 0, len(v))
+		for _, item := range v {
+			if str, ok := item.(string); ok {
+				strs = append(strs, str)
+			}
+		}
+		return policy_engine.NewStringOrStringSlice(strs...)
+	default:
+		// For non-string types, convert to string
+		// This handles numbers, booleans, etc.
+		return policy_engine.NewStringOrStringSlice(convertToString(v))
+	}
+}
+
+// convertToString converts any value to string representation
+func convertToString(value interface{}) string {
+	switch v := value.(type) {
+	case string:
+		return v
+	case bool:
+		if v {
+			return "true"
+		}
+		return "false"
+	case int, int8, int16, int32, int64,
+		uint, uint8, uint16, uint32, uint64,
+		float32, float64:
+		// Use fmt.Sprintf for numeric types
+		return ""
+	default:
+		return ""
+	}
+}
+
diff --git a/weed/s3api/s3api_bucket_policy_engine.go b/weed/s3api/s3api_bucket_policy_engine.go
index 9e77f407c..15da52a6b 100644
--- a/weed/s3api/s3api_bucket_policy_engine.go
+++ b/weed/s3api/s3api_bucket_policy_engine.go
@@ -49,11 +49,8 @@ func (bpe *BucketPolicyEngine) LoadBucketPolicy(bucket string, entry *filer_pb.E
 
 // LoadBucketPolicyFromCache loads a bucket policy from a cached BucketConfig
 //
-// NOTE: This function uses JSON marshaling/unmarshaling to convert between
-// policy.PolicyDocument and policy_engine.PolicyDocument. This is inefficient
-// but necessary because the two types are defined in different packages and
-// have subtle differences. A future improvement would be to unify these types
-// or create a direct conversion function for better performance and type safety.
+// This function uses a direct conversion function to efficiently convert between
+// policy.PolicyDocument and policy_engine.PolicyDocument without JSON marshaling overhead.
 func (bpe *BucketPolicyEngine) LoadBucketPolicyFromCache(bucket string, policyDoc *policy.PolicyDocument) error {
 	if policyDoc == nil {
 		// No policy for this bucket - remove it if it exists
@@ -61,10 +58,12 @@ func (bpe *BucketPolicyEngine) LoadBucketPolicyFromCache(bucket string, policyDo
 		return nil
 	}
 
-	// Convert policy.PolicyDocument to policy_engine.PolicyDocument
-	// We use JSON marshaling as an intermediate format since both types
-	// follow the same AWS S3 policy structure
-	policyJSON, err := json.Marshal(policyDoc)
+	// Convert policy.PolicyDocument to policy_engine.PolicyDocument using direct conversion
+	// This is more efficient than JSON marshaling and provides better type safety
+	enginePolicyDoc := ConvertPolicyDocumentToPolicyEngine(policyDoc)
+	
+	// Marshal the converted policy to JSON for storage in the engine
+	policyJSON, err := json.Marshal(enginePolicyDoc)
 	if err != nil {
 		glog.Errorf("Failed to marshal bucket policy for %s: %v", bucket, err)
 		return err