Introduction: Overweight and obesity in children has been documented to be major health problem. This study is the educational intervention of child`s parents according to the social cognitive theory (SCT) for their body mass index (bmi) decrease in overweight and obese children of pre-elementary grade in Zarrinshahr. Materials and Methods: This quasi-experimental study was conducted on mothers with overweight and obese pre-elementary school children, residents of Zarrinshahrtown in 2015. Mothers were divided randomly into the intervention and control groups (n=45 each). For the intervention group (children and parents), an educational program was designed, based on the SCT and presented in 4 sessions. Data were collected by a researcher made questionnaire, including demographic information, the structures of SCT, and height and weight measurement tools, both before (baseline) and 5 months after the educational intervention. Data were analyzed by Mann-Whitney, Chi-square test, analysis of covariance and the independent t-test. Results: Five months after educational intervention,mean scores of all structures of SCT, including self-efficiency, outcome expectations, self-regulation and social support of the intervention group showed a meaningful increase (P<0.001) in comparison with the control group. Physical activity of children in the intervention group also had a meaningful increase in comparison with controls. Use of social media, sweetmeats, salty snacks and sweet drinks after intervention showed no significant increase. In children, BMI showed a significant difference, compared to the pre-intervention assessment (P<0.05). Conclusion: Results of the present study, showed that the social-cognitive theory can be used cautiously in related studies of children affected to by overweight.