en Effect of Theory of Planned Behavior-Based Education on Fast Food Consumption in Female High School Students Aims: Inappropriate dietary habits, particularly the growing tendency to consume fast food, pose significant health challenges in modern society, especially among adolescents. This study aimed to evaluate the effectiveness of a health education program based on the theory of planned behavior in reducing fast food consumption among female high school students. Materials & Methods: In this study, the sample size was determined to be 38 individuals per group (95% CI and 90% power), but 50 individuals were included to increase accuracy. Thus, cluster random sampling divided 100 students from District 4 of Tehran into control and intervention groups. Data were collected via a valid questionnaire assessed by five health education professors, covering demographic information, knowledge, and theory of planned behavior constructs. The intervention group participated in three 50-minute educational sessions, which included lectures, Q&A discussions, and the distribution of brochures and books. The data were analyzed using SPSS-22, employing statistical tests, such as Kolmogorov-Smirnov, Mann-Whitney U, Chi-square, and independent t-tests. Findings: Following the educational intervention, the mean scores for attitude (p=0.002), subjective norms (p=0.005), and perceived behavioral control (p=0.005) were significantly higher in the intervention group compared to the control group. However, no significant changes were observed in knowledge (p=0.936), behavioral intention (p=0.393), and behavior (p=0.721) related to reducing fast food consumption. Conclusion: The educational program based on the theory of planned behavior is effective in improving attitudes, subjective norms, and perceived behavioral control. Health Education,Theory of Planned Behavior,Fast Food,Students,Female, 81 87 http://daneshafarand.org/browse.php?a_code=A-10-87033-1&slc_lang=en&sid=4