Purpose: This study aimed to estimate the effects of a regular walking exercise program on metabolic syndrome, cardiovascular risk factors, and depressive symptoms among the elderly with diabetic mellitus (DM) based on the Theory of Reasoned Action (TRA). Methods: This study has randomized and stratified experimental design with experimental and control groups. We developed a regular walking exercise program suitable for the elderly with DM based on the guidance of AAHPERD. The experimental group participated in the regular walking exercise program, which contains walking exercise 3 times a week and 50 minutes each time for 3 months and education on controlling diet and preventing complications once a week and 20 minutes each time for 4 weeks. Post-test was conducted after 3 months to estimate metabolic syndrome, cardiovascular risk factors, and depressive symptoms. Results: The regular walking exercise program was effective for decreasing the waist size, the level of fasting blood glucose (FBG) and triglyceride (TG), cardiovascular risk factors and the severity of depressive symptoms among the elderly with DM. Conclusion: The incidence of complications would be decreased by applying a regular walking exercise program.