Background: Today, the consumption of junk food as a snack among children, especially in elementary school students is on the rise. This research has measured Theory of Planned Behavior constructs in this field.

Materials and Methods: This is a cross-sectional and analytical study that was carried out on 217 primary school students in Arak city in 2015. Students were selected according to cluster sampling method. Data collection instrument was a researcher-developed questionnaire consisting of theory of planned behavior constructs such as attitudes, subjective norms, perceived behavioral control, behavioral intention and performance. Reliability and validity of the questionnaire was studied before the study. Multivariate linear regression model was used to determine the most important predictive constructs of students behavior.

Results: In this study, the mean and standard deviation score of attitude (75.41±12.42), subjective norm (78.25±11.20), perceived behavioral control (63.69±17.06), behavicral intention (76.26±15.44), and performance (48.84±24.44) were observed. Based on the results, perceived behavioral control could predict 23 percent change in behavior. There was a direct correlation between the score of constructs and performance(p<0.05). Moreover, there were not any significant differences(p>0.05) between students nutrition and age(r=0.019), weight (r=0.07), height (r=0.12) and BMI (r=0.07).

Conclusion: The results of this study suggested that positive attitude and self-esteem must taken into account to control students diet, in the design of interventions to prevent consuming junk food.