It is widely acknowledged that physical education can play a potentially important role in enhancing public health by creating positive attitudes toward exercise (Ntoumanis, 2001). However, these initiatives will have limited success if students are not motivated to participate actively in physical education. The present study was purposed to utilize the cooperative learning concept of develop a positive learning environment in teaching physical education for junior high school students. More closely, the study was tried to examine the effects of the cooperative leaning concept on student's learning motivation and physical activity levels. In addition, a liner trend of student learning motivation and their physical activity levels after an intervention of cooperative learning concept was also examined. Two intact classes of ninth grade students (n= 64) participated in this study. One class (n=32) served as the treatment group and received four weeks of the traditional physical education class follow by the eight weeks of the cooperative learning strategy. One class (n=32) served as the control group and received twelve weeks of traditional physical education. The participants completed the Learning Motivation Questionnaire (LMQ; as conceptualized by Keller, 1998) before and after an intervention. The digit pedometer was used as the instruments to measure students' physical activity levels during the intervention. The independent t-test was conducted to analysis the learning motivation between two groups. The general liner trend statistic was used to determine an interaction of students' physical activity levels and learning motivation for both groups. The independent t-test analyses indicated that the treatment group had higher scores in the post-test on learning motivation than the control group (t=2.63, p<.05). The levels of physical activity was measured by the digital pedometer indicated that the treatment group had higher steps (2422.16) than the control group (1873.78) during the 12 weeks of intervention. The general liner trend statistic analyses showed that the treatment group has a more liner trend for the interaction of students' physical activity levels and learning motivation during the intervention than the control group (F=127.78, p<.05). However, no significant physical activity levels difference founded in the control group (F=.81, p>.05). To our knowledge, this study provides the first evidence from a randomized controlled trial that manipulate the motivation results in increased physical activity among junior high school students. The results encourage the use of motivation as a targeted, mediator variable in interventions designed to increase physical activity among junior high school students.Keyword(s): exercise/fitness/physical activity, middle school issues