Aims The prevalence of Diabetes type 2 has been increased significantly during recent years. So, prevention is necessary from adolescence. This study aimed to investigate the effect of Health Belief Model-based education on preventive behaviors of Diabetes type 2 in male adolescences. Materials & Methods This semi-experimental study was conducted on 208 secondary school students of Hamadan city (104 students in an experimental group and 104 students in a control group) in 2018, who were selected using the stratified-proportional sampling method. Data were collected using a researcher-developed questionnaire including demographic, awareness, model constructions, and preventive behavior. Afterward, an educational intervention was implemented in the experimental group based on Health Belief Model in four 45-60 minute sessions. After one month, the data were recollected from the two groups and analyzed using Chi-square, t-test, and linear regression by SPSS 16 software. Findings Comparing the scores of awareness, Health Belief Model constructs, and student’ s preventive practices revealed no statistically significant differences between the two groups at the beginning of the study (p>0. 05). However, after the intervention, significant differences were observed between the two groups regarding awareness, the Health Belief Model constructs, and student’ s preventive practices (p<0. 05). Linear regression analysis indicated that self-efficacy was the most important independent predictor of type-2 diabetes-preventative behavior (p<0. 05). Conclusion Health Belief Model-based education is effective in promoting type-2 diabetes prevention behaviors in students.