Theoretically grounded research on the determinants of Arab American children's physical activity is virtually nonexistent. Thus, the purpose of our investigation was to evaluate the ability of the theory of planned behavior (TPB) and social cognitive theory (SCT) to predict Arab American children's moderate-to-vigorous physical activity (MVPA). Children (N = 348, ages 10-14) completed questionnaires assessing the TPB and SCT constructs as well as MVPA. Using multiple regression analyses we were able to account for 9% of the variance in MVPA. Based on standardized beta-weights, variance accounted for, and the significance of F change, we concluded that SCT variables were better predictors of MVPA compared with the TPB constructs. In particular, barrier self-efficacy was the most critical variable within SCT and supports the potentially valuable role that efficacy cognitions play in promoting MVPA in Arab American children. (Contains 2 endnotes and 4 tables.)