The present study examined the effects of swimming on some plasma parameters of lipid metabolism in the middle-aged women. The control group(C) was the women who lived without any intentional physical exercise, and the first experimental group(S I) and the second experimental group(S II) had gone swimming everyday at least one hour for 3-6 months, and more than one year, respectively. The results obtained were summarized as follows: 1) Energy and nutrient intakes of the three groups were not different, but the body fat(%) of two experimental groups(S I, S II) was significantly lower than that of control. 2) Total cholesterol and HDL-cholesterol in plasma were not significantly changed by swimming and swimming period. However, total lipids and LDL-cholesterol were significantly lower in the two experimental groups than in control. 3) The level of plasma triglycerides of SI was not different from the control, but SII showed significantly lower triglycerides. 4) Acid-soluble acylcarnitine and $eta$-hydroxybutyrate concentration in plasma were significantly greater in SII than in control. There results suggest that regular swimming in a longer period might help to protect the risk of obesity and cardiovascular disease by modulating lipid metabolism.