Abstract: The purpose of this study was to determine the effects of aerobic exercise intensity on the quantitative and qualitative changes of serum Low-Density Lipoprotein (LDL). In 2005, thirty low active men aged 25-42 years were randomly allocated to three high intensity (HI, N = 10), moderate intensity (MI, N = 9) and control (CO, N = 11) groups. The high and moderate intensity groups participated in an 8 week aerobic program which consisted of aerobic activities lasting 45-60 min; three times a week at an estimated 75-80% and 60-65% of their age-predicted maximum heart rate, respectively. Both programs began at a prescribed intensity and maintained constant according to the improvement of subjects during the program. In order to control the training intensity, heart rate was monitored and recorded in 10 min intervals by a cardio frequency meter. After 8 week, LDL particle size increased significantly in the MI group whereas, LDL concentration was not changes significantly in the MI group. There were no significant changes regarding LDL particle size and concentration in the HI and CO groups (p>0.05). These data suggest that MI training can be more effective in increasing LDL particle size than HI training.