Outside-school physical activity may shape and reshape students' motivation and mediate their learning in physical education class (Chen & Shen, 2004). However, few researchers have empirically addressed this issue. Using the Self-Determination Theory as a framework, we designed this study to examine the differences between those who participate in outside-school physical activity and those who do not in terms of self-determined motivation in physical education. Participants consisted of 545 9th graders (ages 14-16 yrs, 46.1% females) who completed measures of need support (i.e., autonomy support, cooperative learning, caring, and individual's improvement), need satisfaction (i.e., competence, relatedness, autonomy), motivational regulations (i.e., intrinsic, identified, introjected, and external regulations), and motivational consequences (i.e., physical activity behavior, grade, and future intention to take part in elective PE) in physical education. Information on out-of-school physical activity experiences was also gathered using a survey (Chen & Shen, 2004). Four MANOVAs were conducted to examine participation differences in need support, need satisfaction, motivational regulations, and motivational consequences, respectively. In the analyses, we used gender as a covariate to control its variations and set the alpha at .01 rather than .05, to avoid possible type I error rates. With regard to need support, the main effect for participation status was significant: F (4, 566) = 3.15; p <. 01; partial ©¯2 =.02. Compared with the non-participants, the participants reported significantly higher perceptions of autonomy support provided by the teacher. No differences in cooperative learning, caring, and individual's improvement were found. In relation to need satisfaction, there were significant effects for participation status: F (3, 567) = 21.16; p <.01; partial ©¯2 =.10. Those who participated in after school activities reported significantly greater competence, autonomy, and relatedness need satisfaction. The MANOVA for motivational regulations also showed a significant main effect: F (4, 566) = 9.21; p <.01; partial ©¯2 =.06. Participants displayed a higher intrinsic motivation and an introjected regulation compared to the non-participants. Last, with regard to the motivational consequences, the analysis revealed a significant main effect: F (3, 567) = 11.58, p<.01; partial ©¯2 =.04. Participants reported stronger intentions to take part in elective PE than the non-participants. However, differences in physical activity behavior in physical education class and grade were not found. Our findings support the hypothesis that out-of-school physical activity programs can significantly influence students' motivation and learning behavior. There is a complex and dynamic relationship among outside-school physical activity, motivation, and learning in PE. Keyword(s): high school issues, physical education PK-12, youth sports