Objective: This study compared the effects of a behavioral approach program（BAP）and a knowledge-oriented program（KOP）to promote physical activity and healthy dietary habits in community-dwelling middle-aged Japanese. Both programs were designed to have the same intervention protocol in terms of duration and frequency. Methods: One hundred subjects（81 females）, 57.4 ± 8.3 years of age（mean ± SD）, were randomly assigned to either the BAP or KOP group. The subjects in both groups participated in 2-hr monthly group sessions over a 4 month period. The BAP was based on learning theory and social cognitive theory, and comprised of behavioral strategies（e.g., goal setting, self-monitoring, rewards, and social support）and group discussions. The KOP was based on a conventional health education program, and comprised of lectures on lifestyle-related diseases, physical exercise, and nutrition, followed by group discussions. The primary outcomes included: 1）changes in the number of walking steps, 2）total energy expenditure for exercise and leisure-time physical activities calculated by a self-reported questionnaire, 3）total energy intake of foods, fats, and vegetables, and 4）self-efficacy in physical exercise. Results: A significant inter-group difference existed in the change in number of daily walking steps between the BAP and KOP groups（+226 steps vs. －968 steps, P=0.02）. There were significant improvements in fat and vegetable intake in both the BAP and KOP groups, but there were no significant differences between the two groups. There was no significant change in exercise self-efficacy in either group. The change in exercise selfefficacy positively correlated with the change in leisure-time physical activity in the BAP group（r=0.35, P=0.02）. Conclusion: These findings suggest that the behavioral approach program promoted greater improvement in physical activity than the conventional health education program in community-dwelling middle-aged Japanese adults.