Objective: The objective of this study was to determine obesity prevalence and healthy nutritional knowledge among adolescents. Subjects and methods: Planned cross-sectional onset and intervention afterwards, participants were 6th& 7th grade students. Socio-demographic variables, wealth, perceived body image, nutritional habits and knowledge was questioned face to face. Weight and height was measured and evaluated via BMI percentiles. Nutritional knowledge was determined via 15 multiple choice questions. An interactive nutrition education program consisted of presentation, a game, songs and animated videos were conducted and after the intervention, nutritional knowledge was re-assessed as a post-test. Independent and dependent samples t test, logistic regression analysis, chi-square tests were conducted for analysis. p<0.05 was considered significant. Results: Among 462 participants, 18.2% were obese (24.8% for boys, 11.9% for girls), 68.0% of the mothers were unemployed, 23.8% of the households were in the low wealth group. Nutritional knowledge score increased significantly from 11.75 +/- 2.07 to 12.09 +/- 1.97 (p<0.001). Conclusions: Obesity was more frequent than expected. Nutrition education increased nutrition knowledge significantly. In order to prevent obesity in adolescence, multicomponent, holistic school interventions must be conducted.