Background:In facing the transition period, many adolescents tend to explore their sexuality and engage in risky sexual behavior. This risky behavior is a main contributor to sexually transmitted infections (STIs) and unintended pregnancy. Peer-based intervention is often used in programs that promote sexual and reproductive health in adolescents, including prevention of STIs and unintended pregnancy. This study aimed to examine the effect of peer-based interventin on STI and unintended pregnancy preventive behavior among adolescents.Subjects and Method:This was a meta-analysis study that was carried out according to the PRISMA guidelines. The articles with randomized controlled trial study designs published in 2000-2020 were included for the meta-analysis. Several databases were used in searching for the articles. The articles obtained were screened to obtain the articles that met the eligibility criteria. The articles were analyzed using RevMan 5.4.Results:There were 14 articles that met the criteria for a meta-analysis with a sample size of 18,325. The study showed that peer-based intervention was statistically significant in improving sexually transmitted infection preventive behavior (RR= 1.15; 95%CI= 1.02 to 1.30; p= 0.020) and unintended pregnancy preventive behavior among adolescents (RR= 1.14; 95% CI= 1.00 to 1.30; p=0.040).Conclusion:Peer-based intervention should be considered as an effort to promote STIs and unintended pregnancy preventive behavior among adolescents.Keywords: peer-based intervention, sexually transmitted infection, unintended pregnancyCorrespondence: Denanda Agnes Safitri. Masters Program in Public Health, Universitas Sebelas Maret. Jl. Ir. Sutami 36A, Surakarta 57126, Central Java. Email: denandagnesafitri@gmail.comJournal of Maternal and Child Health (2020), 05(06): 693-704https://doi.org/10.26911/thejmch.2020.05.06.09.