Introduction: Menstruation is the first step of a girl to start her reproductive life. Menstruation is a unique phenomenon to the female. The onset of menstruation is one of the important changes occurring among the girls during the adolescent years. Objectives: Assess the knowledge of adolescent girls regarding menstruation. Assess the practices of adolescent girls during Menstruation Associate the level of knowledge of adolescent girls with their selected socio demographic variables Material and methods: The present community based cross- sectional study was conducted in government girls high school, Kadapa, Andhra Pradesh state (India). The study sample included 60 adolescent girls selected by using simple random sampling technique Results:- It reveals that 5% of adolescent girls had below average knowledge , 42.5% of adolescent girls had average knowledge and 52.5% had average knowledge and practices regarding menstruation among 60 adolescent girls 67.5% are celebrated the attainment of menarche as a function,87.5% practices stoppage of religious activities during periods,77.5% were taking additional foods during periods,57.5% were followed dietary restrictions during periods, 82.5% expressed that they need extra hours of rest during periods. Conclusion: The findings of study revealed that 5 % of adolescent girls had poor knowledge regarding knowledge of adolescent girls regarding menstruation. Educational programme needs to be organized to improve the knowledge of adolescent girls.