Adolescence is a transition period of children into adulthood. Teenagers ranges of 10-19 years. Along with the transition period, teens have a complex problem. One is the behavior of premarital sex. Factors affecting premarital sex among adolescents are lack of information and knowledge about reproductive health. Reproductive health education is a way to reduce negative impacts and prevent premarital sex. The study aims to determine the effect of peer education on knowledge of reproductive health and adolescent attitude in preventin of the pre-marital sex at SMAN 1 Sukamara, Central Kalimantan Province. It is an intervention study with a quasi-experimental design, pre and post test control group design. The samples are 50 students with 25 students at intervention and control groups, respectively. Data are analyszed was performed using paired samples t test and unpair t test. Reproductive health education is given three times. Pre-test and post test was performed to measure knowledge and attitudes. There is a signifi cant difference in the control group and the treatment group on the knowledge and behavior of teenagers. knowledge in adolescents p=0.000 (p<0.05) and attitude in adolescents p=0.014 (p<0.05). There is the infl uence of reproductive health education to improve the knowledge and attitude of adolescent in SMAN 1 Sukamara, Central Kalimantan Province.