This study investigated the effect of 12 weeks\' aerobic exercise program on obese men\'s body composition, blood lipids, C-Reactive Protein(CRP) and Homocysteine by carrying out the program at 60%HRmax five times a week. As research subjects, 14 obese men were selected who were in their late 20s or in their early 30s with over 25% of body fat percentage. This study came to the following conclusion by observing the subjects before the exercise program and 8 weeks and 12 weeks after the exercise program. In the aerobic exercise group, it was found that their weights and body fat percentages significantly decreased after 12 weeks\' program (p<.05). Although there were no significant differences in the body fat percentage, TC, TG, HDL-C, LDL-C, CRP and Homocysteine, there was some change found in the values with positive patterns. Consequently, this research is considered to suggest a new possibility of improving the vascular disorder inducing factors of obese men in their middle 20s or early 30s through aerobic exercise. For further studies, it seems necessary to carry out an accurate observation into obese men\'s exercise types, various periods of exercise, life styles and patterns and even their eating habits, which is different from the research subjects for this study.