Introduction: Type II diabetes mellitus is considered a major health problem due to its complications. The complications could be prevented or delayed with alterations in the patients’ behavior and diet. The aim of the current research was to evaluate the theory of planned behavior (TPB) in the prediction of healthy diet behavior among type II diabetic patients.

Materials and Methods: This cross-sectional study was conducted in a Diabetes Clinic in Zabol, Iran. A total number of 300 diabetic patients (type II) with no complication were selected as participants via random sampling technique. A self –administered questionnaire based on TPB was used to evaluate variables, such as patient’s attitude, subjective norm, perceived behavioral control, intention to eat a healthy diet, and nutritional style. Data were analyzed using SPSS (version 20) through factor analyze.

Results: The results revealed that the TPB fitted the data obtained from the patients with type II diabetes and within dietary behavior. Perceived behavioral control, subjective norm, attitude and intention to maintain a healthy diet were significantly related to healthy diet behavior.

Conclusion: The TPB is a useful theory in determining the intentions of patients with diabetes and their obedience to a healthy diet.