Changing lifestyle and improving self-efficacy are two effective factors in weight loss. Self-efficacy is as a key factor in increasing physical activity. Appropriate lifestyle is another important factor for obesity treatment. In this paper we focus on increasing self-efficacy and changing lifestyle of obese children with the aim of video game. Thereby, a video game has been designed and developed for this purpose. The proposed video game tries to achieve these two factors by preparing challenges for the player to choose the appropriate food for meals and forcing her/him to do specific body exercises. The assessment of the game on a group of children showed their enthusiasm for doing sports activities and influencing their lifestyle.