Background: Obese and overweight children are often cast as being lazy or unmotivated in regards to participation in physical activity. Purpose: Based on the social cognitive principle of triadic reciprocality, this pilot study was designed to examine the impact of a mastery motivational climate on overweight and obese children's commitment to, and enjoyment of, physical activity. Methods: Obese and overweight children ("n" = 43) enrolled in a summer physical activity and nutrition education program incorporating a mastery motivational climate served as participants in this investigation. Pre and post measures of the participants' commitment to, and enjoyment of, physical activity were assessed. In addition, accelerometer data were collected to assess the participants' engagement in physical activity. Results: The findings revealed a statistically significant difference in participants' enjoyment of and commitment to physical activity. In addition, physical activity data demonstrated that the participants engaged in more moderate bouts of physical activity in the program compared to their school-based physical education. Discussion: Obese and overweight children's commitment to and enjoyment of physical activity was stronger as a result of a mastery motivational intervention program. Participation in the program encouraged participants to engage in health-enhancing levels of physical activity. Translation to Health Education Practice: The results of this pilot study support the utilization of a mastery motivational climate to enhance overweight and obese children's participation in physical activity. (Contains 2 figures.)