Based on the Transtheoretical Model, this study investigates the stages of exercise behavior among overweight and obese children, and assesses relationships among behavioral stages and other constructs. Using the definition of obesity for children and adolescents of the Taiwan Department of Health, Executive Yuan (2002), 353 overweight and obese children out of 1,714 school children from two deliberately selected primary schools, aged 11-13 years old, were selected for participation in this investigation. The instruments included Stage of Exercise Behavior Change Questionnaire, Process of Change Questionnaire, Exercise Self-efficacy Scale, and Decision Balance Scale for Exercise. Data were analyzed using frequency, χ^2 tests, one-way MANOVA, one-way ANOVA, and Tukey's Honestly Significant Difference (HSD). The study results are as follows: The majority of the participants were in the preparation stage (50.7%), with only a small minority (7.1%) in the precontemplation stage. About 68.3% did no regular exercise. Furthermore, the mean score for the process of change for exercise was 3.14±0.84 (5 in total), with the highest score being for counter conditioning, while the lowest was for social liberation. Furthermore, the average score for exercise self-efficacy was 43.10±22.64 (100 in total). The average scores for perceived benefits of and barriers to exercise were 3.57±0.54 and 2.44±0.66 (for a total of four), respectively. Participants in different stages differed in scores of the process of change for exercise, exercise self-efficacy, exercise benefits, and exercise barriers (Wilk's Lambda =.637, p＜.001). Scores of process of change for exercise, exercise self-efficacy, and exercise benefits increased from the precontemplation through to the maintenance stage. However, the score of perceived barriers to exercise decreased. The results generally supported the validity of TTM for understanding the exercise behavior of obese children. Thus providing useful information for future studies and exercise promotion programs.