|The research is to discuss the relation between social support and keep-fit self-efficacy in junior high school students' exercise behavior. Also, to realize the differences of social support and keep-fit self-efficacy in background variables. The intentions of this research are as follows. 1. To realize current situation of self-efficiency in junior high school students' exercise behavior. 2. To discuss the differences of social support and keep-fit self-efficiency in background variables. 3. To discuss the relation among social support and keep-fit self-efficiency in junior high students. The samples are from Hsinshe junior high school Students in Taichung. We sent 750 questionnaires by purposive sampling, and got back 625 questionnaires, the recycling rate is 83%. The research tool is questionnaire made by ourselves. The questionnaires include background variables, exercise behavior, social support meter, keep-fit of self-efficacy meter. The results were analyzed by descriptive statistics, Independent-Samples T-test, one-way ANOVE, MANOVA, canonical correlation, stepwise. The major findings were concluded as follow: 1. There are obvious differences in social support and keep-fit self-efficiency among different background students. 2. There's highly correlation between social support and keep-fit self-efficiency.