A growing trend in the meat industry is to produce more with less, which can lead to higher yields without losing the chemical properties of the meat, which determine the price. The aim of this study was to determine the effect of tannin-supplemented diets on the compositional quality of beef. Sixteen male calves were subjected to a productive response test in a feedlot over a 40-day period, with a 30-day adaptation phase prior to the finishing stage of the experiment. Treatments consisted of: a typical cattle finishing diet (control) and a similar diet with 0.3 % extract of condensed and soluble tannins added, providing 1 g of tannin extract per 10 kg of bodyweight. After slaughter, meat samples were taken by cutting transversely between the 12th and 13th rib; the cuts consisted of four 2.5-cm thick chops from each carcass. Samples were analyzed for protein, ash, moisture, fat and dry matter contents using AOAC methods. Results showed that the average content levels were 20.18 % for protein, 5.47 % for fat, 74.35 % for moisture, 2.01 % for ash and 25.65 % for dry matter, for both groups. No significant differences (P ≤ 0.01) compared to the control group were observed; only the fat content was higher than previously reported. Therefore, the tannin concentration used in the cattle diets does not affect the chemical composition of the meat.