Objectives: Adolescent knowledge about sexual and reproductive health (SRH) in Indonesia is low and moderate. This study aims to determine the influence of peer mentorship on improving adolescents' knowledge and attitudes about SRH. Methods: This study uses a quasi-experimental pre- and post-test with a control group design. The population is adolescents in high school, aged 15-19. Eight students were selected as volunteers to be trained by professionals as mentors. The sample was selected using a proportional random sampling technique, with 91 students in each group. Peer mentoring was carried out for three months with 12 meetings. A questionnaire measured knowledge and attitudes before and after the intervention. Results: The majority of respondents were women (57.1 %) and men (42.9 %), with the most common age being 17 years old (29.7 %). There was no difference between the characteristics of the respondents and the variables studied. Respondents' knowledge level increased in the high category after the intervention from 67 to 95.6 %; positive attitudes increased from 48.4 to 51.6 %. Conclusions: Peer mentoring interventions significantly influenced respondents' knowledge. The peer mentoring approach effectively increases adolescents' knowledge and attitudes. It is recommended that this assistance become a school program. © 2025 the author(s), published by De Gruyter, Berlin/Boston.