Eighty Brahman cross bullocks (399.3 ± SD 19.41 kg) were utilized in a 56-d experiment to evaluate the influence of a tannins extract preparation supplementation level on the feedlot performance of feedlot bullocks. Bullocks were individually weighed and blocked by weight. Groups of 5 bullocks were placed in16 dirt-floor pens (6 × 12 m). Pens within a block were randomly assigned to treatments follows: 1) Finishing diet (13.6% CP, 2.11 Mcal NE_m/kg) formulated with ground corn (Control, CTL); 2) Control added with 2 g of tannins extract preparation/ kg of DM (TE2); 3) Control supplemented with 4 g of tannins extract preparation/ kg of DM (TE4); and 4) Control added with 6 g of tannins extract preparation/ kg of DM (TE6). The tannins extract preparation (TE) was provided as TMP Protein Enhancer + ByPro (Tecnica Mineral Pecuaria, Mexico, that contains 50% of condensed and hydrolysable tannin blend. TE treatments were top dress on the diet in the feed bunk. Results were analyzed by ANOVA for a randomized complete block design. Three orthogonal contrasts were performed: I = 0 vs. 2 + 4 + 6 g of TE/kg DM; II = 0 vs. Two g of TE/kg DM; and III = 2 vs. Four + 6 g of TE/kg DM. and the linear, quadratic or cubic trend were tested by polynomial contrasts. The final weight of TE2 bullocks was higher than CTL (P = 0.05), and a tendency for a quadratic response was observed (P = 0.10). TE2 increased 13.8% (P = 0.05) the ADG respect to CTL (1.53 vs. 1.35 kg/d). ADG show a quadratic tendency (P = 0.10). Dry matter intake was not affected by treatments (P > 0.20). Feed efficiency tended (P = 0.06) to be better in TE2 treatment than CTL (0.174 vs. 0.156 kg gain/kg food). Gain/feed ratio responded in a quadratic manner (P = 0.05) as TE supplementation was increased, the best level was calculate by polynomial regression as 3 g of TE by kg of diet DM (R² = 0.3; P = 0.05).It is concluded that performance of feedlot bullocks respond in a quadratic manner to tannins extract supplementary level, and the best response could be expected with addition of 3 g of tannins extract by kg of diet DM.