This study was designed to find out the effects of aerobic exercise on the serum lipids in the middle-aged women. The effects of aerobic dancing on serum total cholesterol(TC), triglyceride(TG) and HDL-cholesterol (HDL-C) were studied in eight sedentary women(control group) and twenty seven aerobic exercising women(aerobic group) , aged 35∼45%. Aerobic exercising subjects were divided into 3 group; 2 to 3 months exercising group(Al), 4 to 10 months exercising group(AH), over 1 year exercising group(AIII) according to the periods of exercise. The serum lipid levels of aerobic exercising groups(AI, AII, AIIII) were compared with those of control group. The results statistically analyzed were summarized as follows : 1) The serum TG levels of aerobic groups decreased very significantly compared with those of control group(p< 0.001) and tended to be lower with the increase in aerobic periods. But there were no significant differences among aerobic groups by ANOVA. 2) The serum TC levels of aerobic groups decreased compared with those of control group and tended to be lower with the increase of aerobic periods. But there were no significant differences among groups. 3) Serum HDL-cholestrol level of A I group was elevated significantly compared with that of control group and significant difference was observed according to the aerobic periods : AR group exhibited higher serum HDL-cholesterol values than AH group, and AH group higher than A I group.