Menstruation is normally exhibit cyclical changes in the ovaries and uterus. Each cycle involves about a month and involves both oogenesis and preparation of the uterus to receive a fertilized ovum. Hormones secreted by the hypothalamus, anterior pituitary, and ovaries control the main events. A quantitative approach with quasi- experimental design was used to assess the effectiveness of structured teaching programme on knowledge and practices regarding menstrual hygiene among adolescent girls of selected schools of Distt. Sirmour, Himachal Pradesh. The sample size was 80 selected by purposive sampling technique. Structured questionnaire to assess the knowledge and practices checklist to assess the practices was used for data collection. The results of the study showed that In control group pre-test mean knowledge score was (7.85) and post-test –test knowledge score was (7.95), pre-test practices score was (13.65) and post-test practices score was (13.75). The difference between pre-test and post-test mean knowledge and practices score were statistically non-significant. In experimental group pre-test mean knowledge score was8.0 and post-test –test knowledge score was 16.15, pre-test practices score was 13.13 and post-test practices score was 17.90. The difference between pre-test and post-test mean knowledge and practices score were highly significant p=0.001. It was concluded that structured teaching program had impact on knowledge and practices regarding menstrual hygiene in adolescent girls. The study findings implied that implementation of structured teaching programme has essential role in improving knowledge and practices of the adolescent girls regarding menstrual hygiene.