Background: WHO reported that, diabetes is a silent killer among chronic diseases, and the prevalence of this disease increases with age. Self-efficacy (SEEF), as one of the constructs of health models, plays an essential role in improving the health and self-management of diabetic patients. Objectives: This study evaluated the effect of the extended parallel process model (EPPM) on the SEEF of type 2 diabetic patients. Methods: This experimental study was conducted on 60 patients randomly divided into two tests (30 people) and control (30 people) groups. The data collection tool was the SEEF questionnaire. In the test group, training was conducted based on EPPM structures in six sessions (45 - 60 minutes) once a week. Routine training was also performed in the control group. The data were analyzed by descriptive statistics (frequency, mean and standard deviation) and inferential statistics (covariance, two independent-samples t-test, paired sample t-test, Fisher and chi-square). Results: Two independent-sample t-test showed no significant difference between the test and control groups before the intervention regarding SEEF (P = 0.45). Meanwhile, a significant difference was observed between the test and control groups regarding SEEF (P < 0.01) after the intervention. The covariance test showed a significant relationship between the effect of EEMP and the SEEF of diabetic patients by removing the pre-test effect (Eta = 0.63, P < 0.01). Conclusions: Based on the results, the developed parallel process model (EEMP) increases SEEF in diabetic patients. This health model is considered an effective and low-cost care method.