Sedentary lifestyle and great advertising of high calorie junk foodstuffs cause the change of the nutritional pattern of children and adolescents. This study has been carried out with this objective: determining the effect of educational intervention based on the theory of planned behavior on reducing consumption of unhealthy snacks in the elementary students in Kermanshah City in 2015-2016. This research is a quasi-experimental study. Research setting was the primary schools in Kermanshah city. Sampling was conducted in multi-stage random method. Three hundred and fourteen female and male students were selected randomly. They were divided into two groups of Case and Control. The data collection tool in this study was a questionnaire. Status of snacks consumption among students in both study groups was examined after four weeks. Descriptive statistics and inferential statistics were used in order to analyze data. Before intervention, there were no significant differences between two groups of case and control. The average grades of the theory of planned behavior structures have increased in case group after intervention and it shows a significant difference (P < 0.05). No significant differences were observed in each structure in control group after intervention. The results indicate the positive effect of educational intervention based on the theory of planned behavior on reducing consumption of unhealthy snacks in elementary students. Theory-based educational intervention has also increased students’ willingness to consume healthy snacks.