Purpose: To improve the oral bioavailability of insulin.Methods: Insulin/S.O complex was prepared under optimal condition; IR and DSC analysis were employed to prove the complex formation; The glucose level was determined by the glucose oxidase method.Results: The insulin complexation efficiency was up to 96.5% with about 80nm mean diameter.There is evident hypoglycemic effect insulin/S.O complex was given by oral administration.Conclusion: The result mentioned above suggested the complex has a potential for oral candidate.