Background: Increased reproductive health problem that occurring in adolescents is one of the causes is lack of knowledge, where knowledge is a factor that influence adolescent behavior in maintaining reproductive health, thus it is necessary to follow-up to improve knowledge about reproductive health. However, it should be noted also with information obtained by adolescents, incorrect information will affect adolescents to behave improperly so it is important for adolescents to have knowledge in which adolescents can avoid deviant behaviors on reproductive health. Research Objective: This study aims to determine adolescent of knowledge on the behavior of maintaining reproductive health in adolescents. Research Methods: This study used a qualitative method with a phenomenological approach and purpose sampling technique. Data retrieval is conducted by conducting in-depth interviews with participants assisted with an interview guide instrument containing open questions where there were four participants in this study. The validity of the data is done by source triangulation. The study used data analysis with seven stages of Colaizzi. Research Results: The results of this study indicate knowledge in maintaining reproductive health in adolescents is good knowledge where adolescents become more aware about reproductive health. Conclusion: The conclusion obtained in this study is that adolescents know that knowledge can influence adolescent behavior in maintaining reproductive health where the importance of knowledge to maintaining reproductive health according to participants to avoid the risks that cause problems in the reproductive health system.