It is known that appropriate exercise changes body composition and improves coronary artery disease. This study was undertaken to evaluate the relationships between aerobic exercise, body composition, and the blood lipid levels in the middle-aged women(33 to 54 years old). The 57 subjects were divided into two groups based on their exercise: the aerobic exercise group(A group: 44) which performed at about $60\%$ of $VO_2max$ during over 6 months and the sedentary one(S group: 13). The percentages of body fat waist/hip ratio(WHR), body mass, and lean body mass of two groups were measured and compared in serum HDLC level and oxidized LDL level, the two most effective factors of coronary artery disease. The subjects in A group showed the lower percentages of body fat and WHR, when compared with the ones in S group. The body mass and lean body mass of A group subjects were higher than those of S group subjects. The serum HDL-C level$(58.6pm12.7mg/mL)$ was significantly higher for A than S group subjects.(p<0.05) The sem ox-LDL level $(6.64pm4.11Eu/mL)$ for A group subjects was lower than S group ones. The fat mass showed significantly positive correlations with atherogenic index(AI)(r=0.301, p<0.05), and with blood glucose levels(r=0.334, p<0.05). Also the WHR whowed significantly positive correlations with LDL-C levels(r=0.277, p<0.05), and with AI(r=0.466, p<0.01). In summary, the subjects in A group have the lower percentages of body fat and WHR, when compared with the ones in S group. Also, A group subject showed a tendency that exercise enhances serum HDL-C levels and decreases oxidized LDL levels. And aerobic exercise showed positive results which change body composition and improve blood lipid levels. There were significantly positive correlations among the percentages of body fat At and blood glucose level. These results suggest that moderately intensive exercise is a significant factor in reducing coronary artery disease.