Adolescence is a very crucial period in which rapid physical, biological, emotional, and psychological changes occur. Therefore, adolescents need complete, accurate, and age-appropriate sexual and reproductive health information. This study was aimed to identify the knowledge and attitude on sexual and reproductive health among adolescents. It is a descriptive cross-sectional study carried out among 440 adolescents from four public schools of Lalitpur, Nepal. A structured Self-administrated questionnaire was applied to collect information. Descriptive and inferential statistics were employed to analyze the data. Out of 440, more than half (53.4%) of respondents had adequate knowledge on sexual and reproductive health with the mean age 17.76+8.74 years. Adolescents who were studying grade 12 (OR=1.654, CI: 1.126-2.429) had significantly higher knowledge than those of grade 11 (p =0.010). The majority (85.9%) of adolescents had proper knowledge about the correct meaning of reproductive health. However, only 43.4% of respondents were aware that HIV/AIDS is not a curable disease. All most participants (87.3%) agreed that men can have sex before marriage, and 73.1% disagree that women should not have sex before marriage. There was a significantly positive relationship between the knowledge and attitude of sexual and reproductive health (p =0.000). This study established the adequate knowledge and positive attitude on sexual and reproductive health where the higher education of adolescents found a significant factor for the knowledge gaining on sexual and reproductive health. So, there needs to be sexual education in the school's curriculum, and this message should be disseminated through teaching, mass-media campaign, social network, and other effective platforms.