Background There are approximately 1.7 million young people globally, with 86% living in developing countries. Inter-census population survey results (SUPAS) in 2015 showed that the population aged 15-24 years old reached 42,061.2 million or 16.5% of the total population of Indonesia. The significant number of adolescents’ population will affect the development of social, economic, and demography aspects nowadays or tomorrow. Limited knowledge and inadequate understanding of reproductive health information can lead adolescents to risky sexual behavior.

Method This was a cross-sectional, descriptive survey among junior high school students of SMPN 7 Nganjuk. The study enrolled 108 students in SMPN 7 Nganjuk, who were selected by stratified random sampling. Data were explored, analyzed, and percentages used to quantify the level of knowledge. Pearson’s chi-square was used to measure associations between categorical variables and independent t-test used to measure the means and relationships of continuous variables.

Result Of the 108 participants, 105 (97,2%) did not know that semen is emitted from the male reproductive tract, and that contains sperm cells, which are capable of fertilizing the female eggs. Besides, 90 (83,3%) participants did not know in what condition they have to go to health workers. Overall, the results showed that only 1 (0,9%) of the participants were highly knowledgeable about adolescent reproductive health, while 28 (26%) and 79 (73,1%) had medium and low levels of adolescent reproductive health.

Conclusion This study showed that adolescents in Junior High School showed inadequate comprehension in reproductive health knowledge. It is crucial to conceive schools as the foundation for providing sexual and reproductive health education among adolescents supported by a friendly and responsive health system. Through adequate reproductive health knowledge, adolescents would understand the risk and responsibility of their sexual behavior.

Keywords: knowledge level, reproductive health, adolescents