Background: Child obesity is one of the main health problems all across the world, which leads to mental and physical health problems. Various models are used in designing intervention to prevent child obesity, one of which is social-cognitive theory (SCT). The constructs of social-cognitive theory are commonly used for designing preventive interventions. However, there is no specific tool based on the constructs of social-cognitive theory to assess the factors associated with child obesity. Aim: The aim of this study was to investigate the validity and confirmatory factor analysis of a SCT-based questionnaire for assessing obesity preventing behaviors among 4-6 years old children. Method: A cross-sectional study was first conducted in 2016 on 240 preschool children aged 4-6 years in Behbahan city (a city in southwest Iran) to assess the obesity prevention behaviors among them using a SCT-based questionnaire. To investigate the validity and confirmatory factor analysis of the SCT-based questionnaire, content and face validity as well as forward-backward translation method were used. Reliability of the questionnaire was also measured by Cronbach’s alpha coefficient and Intra-class Correlation Coefficient (ICC). Construct validity was assured by confirmatory factor analysis. To measure the obesity prevention behaviors in 4-6 years old children, the construct of SCT, including environment, emotional coping, outcome expectations, goal setting and self-efficacy were used. Also, the obesity prevention behaviors used in the model included physical activity, consumption of fruit and vegetable, consumption of sugar-free drinks, and screen. Results: Results of this study confirmed the acceptable content and face validity of the SCT-based questionnaire. The results of confirmatory factor analysis also confirmed the factor loading of more than 0.3 for all variables; therefore, the SCT-based questionnaire had an acceptable validity and reliability. Conclusions: Since the SCT-based questionnaire had an acceptable validity and reliability, it can be used to assess the obesity prevention behaviors in 4-6 year old children, and also to design relevant educational interventions. Keywords: Validation, Social-Cognitive Theory, Behavior, Childhood obesity, Preschool, Prevention