This study is a descriptive research attempted to examine the exercise practice of junior high school students and figure out their changing process, decision-making balance, and self-efficacy according to the exercise practice so that they can be utilized as fundamental data for developing exercise intervention programs for junior high school students. The study subjects were students from five junior high schools in B City. Total 600 questionnaires were distributed, and 554 responded ones were analyzed. The collected data were analyzed using SPSS/Win 10.0. According to the results of analyzing the subjects with the exercise changing stage tool, exercise non-practice group including the precontemplation stage, contemplation stage, and preparation stage occupies 57.6% while the exercise practice group including the action stage and maintenance stage consists of 42.4%. And according to the results of discriminating analysis setting total 10 factors of transtheoretical model variables as predictive factors to predict each group based on whether they practice exercise or not, it was found out that the subordinate factors of the changing process, consciousness-raising (F=33.98, p=.000), self-cognitive decision (F=21.55, p=.000), contrary condition provision (F=84.67, p=.000), helping relationship (F=28.52, p=.000), reinforced thinking (F=14.15, p=.000), and stimulus control (F=54.64, p=.000), and the subordinate factors of the decision-making balance, beneficial factors (F=15.65, p= .000) and hindering factors (F=8.58, p=.004), and self-efficacy (F=78.60. p=.000) were significant predictive factors and discriminating variables. Based on the research findings above, it will be necessary to develop exercise intervention programs sufficiently reflecting the changing process, decision-making balance, and self-efficacy suitably for the subjects and make strategies to encourage their active participation and exercise maintenance, through verifying transtheoretical model variables according to whether the junior high school students practice exercise or not.