The purpose of this study was to discriminate the stages of exercise change by self-determination. The subjects of this study were 176 male and female members selected from an exercise club in Chiayi, and the mean age of the subjects was 38.21±9.58. The subjects were divided into ”precontemplation-contemplation”, ”preparation”, and ”action-maintenance” by ”A Questionnaire of Stages of Exercise Change”. The external regulation, the introjected regulation, the identified regulation, the intrinsic regulation, and self-determination were assessed by ”A Questionnaire of Behavioral Regulation in Exercise”. The results of discriminant analysis indicated that self-determination and intrinsic regulation could discriminate the stages of exercise change, and correctly classified percentage was 91.03. The results showed that self-determination was an important variable in understanding the stages of exercise change.