This study attempts to identify the effects of distance runners’ detraining on the serum lipid metabolism. To do this, the sample of 22 athletes are divided into three groups : the group without any change in their exercise and diet ; the group who stop exercise and reduce the intake of food: and the group who keep exercising but reduce the intake of food. These three groups are repeatedly compared and measured for twelve weeks to see cardiovascular organs and during exercise through different types of training, which leads to following conclusions. 1. For twelve weeks, groups of Training I and Training II show the tendency of decreased serum Total Cholesterol and LDL-Cholesterol, while the group of Detraining revealed increased serum Total Cholesterol and LDL-Cholesterol. The differences among three groups appeared statistically significant at 0.05 level, but the differences between training periods and the interaction effects between the groups and the periods are not statistically significant. 2. For twelve weeks, groups of Training I and Training II show the tendency of increased serum HDL-Cholesterol, while the group of Detraining revealed decreased serum HDL-Cholesterol, while the group of Detraining revealed decreased serum HDL-Cholesterol. The differences among three groups appeared statistically significant at 0.05 level, but the differences between training periods and the interaction effects between the groups and the periods are not statistically significant. 3. For twelve weeks, groups of Training I and Training II show the tendency of decreased serum Triglycerides and TC/HDL-C Ratio, while the group of Detraining revealed increased serum Triglycerides and TC/HDL-C Ratio. The differences among three groups and the interaction effects between the groups and the periods appeared statistically significant at 0.05 level, but the differences between training periods are not statistically significant. 4. These serum lipid lipoproteins which affect VO₂max are Total Cholesterol, HDL-Cholesterol and TC/HDL-C Ratio. (P<0.05)