This study examined the relationship between children's physical activity participation and psychological well being in Hong Kong. The participants were 976 children (Male=513, Female=463), age range was 9-14 years old, the average age was 10.99. The Profile of Mood States inventory (POMS) (McNair Lorr, & Drppoleman 1971) and the global assessment of life measure (Self-Anchoring Scale, Cantril, 1965) were utilized. The mean and standard deviation of the six identifiable mood states for all participants were: Tension-Anxiety (T) (M=49.47, SD=9.58), Depression-Dejection (D) (M=49.58, SD=9.63), Anger-Hostility (A) (M=49.49, SD=9.58), Vigor-Activity (V) (M=49.47, SD=9.58), Fatigue-Inertia (F) (M=49.47, SD=9.58), and Confusion-Bewilderment (C) (M=49.47, SD=9.58). Independent group multivariate analysis of variances (MANOVA) were used to compare the mean vectors among the six dimensions of the POMS. The mood states for males and females were similar. Significant differences were found in depression (F=3.6, p=.028), fatigue ((F=3.7, p=.024), tension (F=3.2, p=.042) and vigor(F=20.1, p=.000). Individual with higher physical activity has higher score in vigor and lower scores in depression, tension and fatigue. Positive relation was found between the total global mood state and life satisfaction. This study supports that physical activity would be beneficial to the psychological well being of children. Therefore, it is essential to encourage children to have active life style.Keyword(s): exercise/fitness/physical activity, recreation