BackgroundThe prevalence of type 2 diabetes is increasing among adolescents and clear strategies are needed to prevent it. The aim of this study was to determine the effect of peer education on knowledge, health beliefs and preventive behaviors of type 2 diabetes in female adolescents.MethodsIn this cluster randomized trial study, 168 students (84 people in each group) were enrolled. The data collection instrument was a questionnaire of knowledge (30 questions), health beliefs (16 questions) and behavior (20 questions) whose validity and reliability were confirmed. Then eight capable students were chosen as peer educators after being trained. The intervention group received 8 sessions of 90-min education through training, lectures, question and answer, and group discussion and with teaching aids such as pamphlets, educational clips and text messages. The post-test was administered two months after the treatment. Data collected using software SPSS16 and Chi-Square and ANCOVA test were used.ResultsThe result showed that the mean and standard deviation of general knowledge, disease symptoms, behavioral risk factors, mid-term outcomes and long-term outcomes, perceived self-efficacy, behavioral beliefs, perceived susceptibility, perceived severity, prevention of stress, healthy food/healthy diet, unhealthy food/unhealthy diet, high-risk behavior, and self-care in the intervention group has increased significantly 2 months after intervention compared of control group (P< 0.001).ConclusionsPeer education increased knowledge and improved adolescents' health beliefs and behaviors. Therefore, training in adolescence in order to prevention of diabetes can be considered as an effective step, and the use of peer-led education in this field is recommended.Trial registrationTrial registration number IRCT20200811048361N1 from School of Public Health & Neuroscience Research Center—Shahid Beheshti University of Medical Sciences. Date applied: 30/12/2020. Date assigned: 01/12/2020.