The aim of the experiment was to investigate the effect of adding flax seed to the cattle diet in the final stage of fattening. A total of 30 male Simmental cattle of uniform initial weight were selected for the trial, which were divided into 2 groups (KON (control) and LS (experimental)). Animals in the control group did not consume flax seed as a dietary supplement, and animals in the experimental group consumed flax seeds in the amount of 3.75% of the concentrated portion of the meal in the last 90 days of fattening, i.e 300 g per day. After slaughtering and cooling, the left carcass side was cut into basic parts according to the Regulation. The study included examination of the tissue fraction of parts of the carcass of the young, determined by dissection. The results of the study showed that the addition of flax seed in the diet had no statistically significant effect on the composition of the carcass parts of the young bulls at the end of the experiment.