Diet control has been an important integrant part of diabetic treatment programs. However, studies have reported that diet control is the most difficult component of the diabetic self-management program for diabetic patients to follow. Many researches support the positive effects of behavioral modification on diet control. In this paper, we designed a diet behavioral modification protocol and applied this protocol to a patient with type 1 diabetes based on the transtheoretical model. Initial results indicate that this protocol helps this patient improve her HbA1c value.