In an experiment carried out on 28 fattening pigs allocated to four groups, the animals were fed with mixtures containing 4.0% fish oil and linseed oil (1:1) supplemented with ascorbate or ascorbate and α-tocopherol acetate. Daily weight gain and slaughter traits were evaluated, as was the chemical composition of the longissimus dorsi muscle. The highest daily weight gain was observed in groups of animals fed mixtures with oil and oil with ascorbate and α-tocopherol acetate. There were no significant differences in backfat thickness and loin eye area. Also the dry matter and fat content in M. longissimus dorsi were similar. The protein content was relatively higher in animals fed the control diet and the diet supplemented with oil and ascorbate.