Small, dense low density lipoprotein (LDL) has been suggested to be highly atherogenic as a result of their low-binding affinity to LDL receptors, their prolonged plasma half-life and low resistance to oxidative stress. Although marine n-3 polyunsaturated fatty acids (PUFAs) have beneficial effects for the prevention of cardiovascular diseases, there is little information on detailed fatty acid composition in LDL particles. In the present study, LDL subfractions were isolated from the plasma of 45 clinically healthy Japanese women by density gradient ultracentrifugation using a light fraction of 1.025-1.034 g/ml (LDL-I), an intermediate fraction of 1.034-1.044 g/ml (LDL-II), and a dense fraction of 1.044-1.060 g/ml (LDL-III). A clear relationship between the frequency of fish intake and increases in plasma n-3 PUFAs was apparent. Although plasma n-3 PUFAs in women with small-sized LDL using non-denaturing gradient gel electrophoresis (GGE) did not show a significant difference, n-3 PUFAs and n-3 PUFAs/n-6 PUFAs in dense LDL-III subfraction increased in the small-sized LDL group using GGE, compared to those with buoyant LDL particles. The result of enriched n-3 PUFAs in dense LDL subfraction suggests that n-3 PUFAs may help prevent atherosclerosis in the arteries of Japanese women with small-sized LDL.