The study was conducted on 32 crossbred fatteners (Polish Landrace ´ Polish Large White) ´ Pietrain fed on a feed containing 0 or 6 % soybean oil after they reached 70 kg of body weight. The fatteners were slaughtered at 0, 12, 24 and 36 days after commencement of feed administration. Feed supplementation with soybean oil did not cause any significant differences in daily gains or feed conversion per 1 kg of live weight. After 24 days of feeding of the animals with feed containing soybean oil, highly statistically significant (P< 0.01) increase (3.0%) in the content of polyunsaturated fatty acids (PUFA) in backfat was noted, while after 36 days of the feeding, contribution of saturated fatty acids (SFA) to total content of fatty acids was significantly lower (6.0%) (P< 0.05) than the respective value at the beginning of the feeding. On the other hand, no significant changes were found in backfat fatty acid profile with respect to monounsaturated fatty acids (MUFA).