The increasing prevalence of childhood obesity is a global public health concern. Numerous experts have noted that comprehensive treatment methods are required to address this complex condition. The Children’s Health and Activity Modification Program (C.H.A.M.P.), a 4-week intervention delivered in a unique camp-based format, was developed for children with obesity and their families using a multidisciplinary approach. The purpose of the current study was to investigate the short- (i.e., 1-week post-intervention) and longer-term (i.e., 3-, 6-, and 12-months post- intervention) effects of C.H.A.M.P. on children’s self-reported: (a) task and barrier self-efficacy; and (b) home-based physical activity. A secondary purpose was to determine whether task and/or barrier self-efficacy served as predictors of self-reported home-based physical activity at any of these time points. The Physical Activity Questionnaire for Older Children (PAQ-C; Crocker, Bailey, Faulkner, Kowalski, & McGrath, 1997) was used to assess self-reported home-based physical activity and modified versions of the Self-Efficacy Scale and Barrier Efficacy Scale (McAuley & Mihalko, 1998) were administered to children to assess task and barrier self-efficacy, respectively. Forty participants (36 different children) completed Year 1 (n = 15; Mage = 10.6; 53% female) and/or Year 2 (n = 25; Mage = 10.6; 56% female) of the program. Results showed that participation in C.H.A.M.P. was associated with significant increases in task and barrier self-efficacy from pre- to post-intervention, after which mean values remained significantly higher than baseline at the 3- and 6-month follow-up assessments. No significant changes were observed from baseline to any of the post-intervention time points for home-based physical activity. Linear regression analysis revealed that task and barrier self-efficacy explained between 18% and 34% of the variance in self-reported home-based physical activity scores. While task self-efficacy contributed more towards the prediction of home-based activity at baseline, 1-week post-intervention, and 3-months post-intervention, barrier self-efficacy emerged as the predominant predictor at 6- and 12-months post-intervention. These results suggest that efficacious beliefs to be physically active and to overcome physical activity-related barriers may be important in the prediction of self-reported home-based physical activity in children with obesity. Taken together, the current findings also emphasize the importance of targeting self-efficacy as a first step towards increasing physical activity in this young population. Keywords. childhood obesity; physical activity; self-efficacy; C.H.A.M.P.; community-based intervention.