Menstruation is a normal physiological process that is managed differently according to various social and cultural understandings.The present study aimed to assess the knowledge, practice and identify on beliefs about menstruation of the adolescent school girls in Seiyun city-Yemen. Cross section study design was used. The sample was 498 girl students in reproductive age 12 to 20 years with mean of 14.8 ± 1.6 years. Self-administration data was collected by using interview questionnaire(sociodemographic data, knowledge of the students about menstrual cycle and disorders, practice regarding menstruation and beliefs towards menstruation) after completing the questionnaire collection from all students in each schools, every participant student adolescent girl was given a brief/summarized pamphlet illustrates the basic information about anatomy of female reproductive system, reproductive cycle, healthy practices and negative attitude. Recommendation: It can be concluded that there are poor knowledge and relatively good hygienic practices among girls that requiring action by conducting directed educational programs.