ABSTRACT The present study was aimed at assessing the effectiveness of structured teaching programme on knowledge regarding menstruation among adolescent boys of selected high school, Muvattupuzha. The objectives of the study were to find out the effectiveness of structured teaching programme on knowledge regarding menstruation among adolescent boys, determine the association between knowledge regarding menstruation and selected demographic variables. The conceptual framework applied for the study is Bertalanffy’s general system theory. A pre-experimental one group pretest post-test design was used for this study. A total of 50 adolescent boys were selected through non probability convenient sampling from Nirmala Public School, Muvattupuzha. The tool used for data collection was a structured questionnaire to assess knowledge regarding menstruation among adolescent boys. Result of the study revealed that that 2% adolescent boys had good knowledge on menstruation while 44% boys had average knowledge and 54% students had only poor knowledge on menstruation in pre-test. On post-test 54% boys had good knowledge, 42% boys had average knowledge and 4% boys had only poor knowledge on menstruation. The structured teaching programme on menstruation was effective in producing significant difference in the knowledge regarding menstruation among adolescent boys. Knowledge regarding menstruation among adolescent boys was significantly associated with previous knowledge about menstruation