Anemia is a great  public health problem worldwide and is often ignored in both developed and developing countries.  The adolescent girl still residue  young planet that neither gets light or water, she remains the flower that could have blossomed but did not. The prevalence of anemia among adolescent girls in India is the highest in the world. Anemia among adolescent girls may lead to delayed attainment of all aspects of development.(Rati et. al. (2014))Objectives : To identity the prevalence of anemia and assess the effectiveness of structured teaching programme on knowledge regarding prevention of anemia among adolescent girls  age group12-18 years studying in a selected government school Jhajjar, Haryana. Material and Methods:The study was conducted at government Sr. Sec. School, Bharana (Jhajjar) Haryana- 124508. The target population of the study was the adolescent girls age group 12-18 years. 100 adolescents girls was selected for the study by using non- probability convenient sampling technique. Result: The finding of the study revealed that prevalence of anemia results had Mild anemia in girls were 61%, Moderate anemia were 39% and Severe anemia were  0%.knowledge  pre test result was 25% of girls had poor knowledge score 75% of girls had average and 0% of girls had good  score on knowledge regarding prevention of anemia among adolescent girls age group 12-18 years, post-test 17% of adolescent’s girls had average and 83% of adolescents girls had good knowledge score on knowledge regarding prevention of anemia among adolescent girls age group 12-18 years. comparison of pre test and post knowledge score to assess the effectiveness of Structured teaching programme in terms of gain knowledge scores among adolescent girls age group 12-18 years ant it was concluded that Structured Teaching Program was effective to improving knowledge regarding prevention of anemia among adolescent girls  age group12-18 years.