To evaluate the effects of zilpaterol hydrochloride (ZH) and a mineral-yeast (MY) mixture two experiments were conducted on finishing steers. Four treatments were: 1) control; 2) MY (chromium, selenium and zinc yeast); 3) ZH; 4) YM+ZH. 125 and 800 g/ton of Zilmax© (ZH) and Bioplex© (MY), respectively, were supplemented to the total mixed ration (TMR). Four beef steers (420±32 kg) fitted with ruminal cannulae and 20 BrahamanxSwiss beef steers (375±6 kg BW) divided in four equal groups were used in the two experiments, respectively. Ruminal pH, volatile fatty acids, ammonia N and DM degradability were not affected (P > 0.05) by treatments. After 40 d of feeding ZH alone or with MY improved average daily gain (ADG) and feed conversion (F:G). Dressing percentage (hot and cold) were higher (P < 0.05) in supplements fed steers and the highest values were observed with MY+ZH. Our results suggested a beneficial synergetic effect of zilpaterol hydrochloride (ZH) and mineral-yeast (MY) mixture on growth, feed efficiency and carcass characteristics of finishing steers.