Background: Nutrition and medical care prevents the incidence and increase of complications in patients with diabetes. There are controversial believes about the effect of education on the knowledge, attitude and practice of patients with type 2 diabetes. This study aimed to assess the effectiveness of education on knowledge, attitude and nutritional behavior of these patients. Methods: In an interventional study, 80 patients with type 2 diabetes were selected from the Tehran Abouzar Clinic (Iran) and allocated randomly in two intervention and control groups. Data collection was conducted before and 3 months after the intervention using a questionnaire including two sections, demographic information and questions assessing the knowledge, attitude, and nutritional behavior. The intervention was nutritional care education during two group discussion-based sections in 30 minute and by a two weeks interval. Results: After the educational program, knowledge about nutrition increased significantly in both case and control groups, which was probably due to the routine education program in that center. But significant increase in attitude and behavior was only observed in the intervention group. Conclusion: Appropriate educational programs should be performed in type 2 diabetes clinics to promote attitude and behavior as well as knowledge of the patients.