The study was conducted on 32 crossbred fatteners (Polish Landrace x Large White Polish) x (Duroc x Pietrain). Fatteners belonging to group S were fed the compound feed with a 6% supplement of soybean oil during the fattening period (30-100 kg) while fatteners assigned to group L were fed the same feed until they reached 70 kg of body weight. At this point, the soybean oil supplement was changed to a 6% supplement of lard. To evaluate fatty acid profiles in loin, 4 fatteners from each group were slaughtered after achieving 70, 80, 90 and 100 kg of body weight. In the loin of fatteners fed over the entire fattening period with soybean oil in the feed mixture, the content of SFA at 100 kg of body weight was significantly lower (p<0.05) than at 70 kg of live weight and the content of PUFA at 90 kg (p<0.05) and 100 kg (p<0.01) was higher. However, no significant change was found in the MUFA content in loin during any part of the fattening period. In fatteners fed the mixture with a supplement of lard, a higher content of SFA at 100 kg of body weight (p<0.05) and lower content of PUFA (p<0.05) was found. The level of MUFA did not change during fattening. MUFA n-6:n-3 ratio in fatteners fed a diet with the share of soybean oil was significantly lower at 90 kg of live weight (p<0.01) than at 70 kg of body weight. No significant change was found in PUFA n-6:n-3 ratio in fatteners fed a diet with lard supplementation.