Sixteen pigs averaging 81.4 kg were assigned to a control diet and three test diets containing 2, 4, or 6% fish oil. Subcutaneous fat samples from the loin were obtained by biopsy at weekly intervals and analyzed for fatty acid composition. The pigs were maintained on the diets (ad libitum access to feed) for 4 wk before slaughter at an average weight of 107.8 kg. Outer and inner layers of backfat, perirenal fat, and intermuscular fat were obtained from the carcass and analyzed for physicochemical characteristics. In the biopsy samples, the contents of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) in fat from pigs fed fish oil began to increase during the 1st wk. Rates of increase were greater during the first 2 wk than during the last 2 wk. In the carcass samples, the increase in EPA and DHA in all fat tissues analyzed became greater as the supplemental levels of fish oil were increased in the diet, whereas oleic and linoleic acids tended to be decreased by increases in EPA and DHA. Color of fat was not significantly different among the control and fish oil groups. With the increase in fish oil in the diet, the hardness of fat measured with a texturometer was decreased. The refractive index and the iodine number were increased. As for differences among anatomical locations, it was noted that EPA and DHA contents of perirenal fat were higher than those of backfat and intermuscular fat. These results indicate that porcine adipose tissues rich in EPA and DHA can be produced by feeding fish oil.