INTRODUCTION: The word ‘’Adolescent’’ is derived from the Latin word ‘adolescere’ which means to grow to maturity that indicate the defining features of adolescence. During puberty the physical changes occur which transform the body of child into that of an adult, changes in body size, and changes in body proportions. Adolescent period is the formative period when maximum amounts of changes take place and pubertal change is one of them. The main pubertal change that occurs in girls is menstruation. This is an important landmark in the process of growth and maturation and prepares them for motherhood. Yesterday’s girl is today’s adolescent and tomorrow’s mother. (1) AIM OF THE STUDY: Assess knowledge regarding menstruation and menstrual hygiene among adolescent girls MATERIAL AND METHOD: A Quasi-experimental one group pre-test post-test study was used in order to evaluate effectiveness of structured teaching programme (the Independent variable) on knowledge regarding menstruation and menstrual hygiene (the dependent variable) among adolescent girls of selected by purposive sampling technique school of Jodhpur. Each participant was informed about the study and that they could withdraw at any time and a written consent was also obtained. RESULT: The findings of the study reveals that in pre-test majority (54.17%) in the experimental group and 91.67% in the control group were having below average knowledge and 45.83% in the experimental group and 8.33% in the control group were having above average knowledge. However the majority of the demographic variable such as age, religion, age of menarche, type of family, educational status, educational status of mother, and sources of information were found not significant association with the level of knowledge regarding menstruation and menstrual hygiene among adolescent’s girls except place of residence, monthly family income. CONCLUSION: It can be concluded that there was a significant improvement on the post-test level of knowledge after implementing STP. This indicates that STP was effective in increasing the knowledge of adolescent girls.