Statement: A study to assess the effectiveness of Self Instruction Module on knowledge and practice regarding harmful effect of Junk food among adolescents in selected school at selected city. Objectives: 1. To assess the existing knowledge regarding harmful effect of Junk food among adolescents. 2. To assess the existing practice regarding harmful effect of Junk food among adolescents. 3.To correlate the knowledge and practice regarding harmful effect of Junk food among adolescents. 4. To assess the effectiveness of Self Instruction Module on knowledge and practice regarding harmful effect of Junk food among adolescents. 5. To find out the association between post-test knowledge score with their selected demographic variables. 6.To find out the association between post-test practice score with their selected demographic variables. Research Methodology: evaluative research approach was used with pre experimental one group pre-test post-test design population was 30 adolescents, non- Probability purposive sampling technique was used for data collection. Result: In pre-test, the majority of 15(50%) of the adolescents were having poor knowledge, 9(30%) of the adolescents were having average in knowledge, and 6(20%) of the adolescents were having good in knowledge regarding harmful effect of Junk food. In post-test, the majority of 17(56.7%) of the adolescents were having average knowledge, 10(33.3%) of the adolescents were having good in knowledge, and 3(10%) of the adolescents were having poor in knowledge regarding harmful effect of Junk food among adolescents. Conclusion: The study was drawn Percentage distribution of adolescent according to their level of knowledge and practice showed they had average Self Instruction Module on knowledge and practice regarding harmful effect of Junk food.