Tannins are plant polyphenols with the capacity to form complexes mainly with proteins reducing their degradation in the rumen and, thus, have the potential to increase the metabolizable protein supply and/or to decrease the urinary N losses by ruminants. However, tannins might also decrease feed intake and digestibility. Moreover, the nutritional effect of tannins is dependent on the tannin source. Six Texel wethers (67.0 ± 6.53 kg) fed ad libitum Tifton hay (Cynodon sp.) and 12 g/kg body weight (dry matter (DM) basis) of concentrate were used in a crossover design with 2 21 d periods to evaluate the effect of dietary inclusion of a tannin extract from Acacia mearnsii on feed intake, digestibility and N excretion. The concentrate was composed of cracked corn grain (0.36), wheat bran (0.36) and soybean meal (0.28) with or without 10 g/kg DM of tannin extract of Acacia mearnsii. Total feed, refusals, feces and urinary excretion were measured during the last 7 d of each experimental period. The concentrate represented in average 0.40 of total DM intake. Total intake (g/day) of organic matter (OM, 1720 ± 132.0), neutral detergent fiber (NDF, 1039 ± 78.8) and N (38.2 ± 3.29), as well as the apparent digestibility of OM (0.77 ± 0.031), N compounds (0.82 ± 0.020) and NDF (0.72 ± 0.038) and urinary N excretion (21.4 ± 2.33 g/day) were not affected by tannin extract inclusion. Tannin extract reduced (P < 0.05) the proportion of fecal N from endogenous origin (0.81 vs 0.76) and the true digestibility of N compounds (0.97 vs 0.95). These results indicate that tannin inclusion can affect N digestion. Further studies are needed to optimize the amount of tannin for each diet.