The purpose of this study was to evaluate the effect of replacing soybean meal with treated castor meal with (CMT) or without lime (CMNT) on the nutrient intake, performance, carcass characteristics, and yield of commercial cuts of beef cattle from a feedlot. Thirty male, castrated, crossbreed zebu cattle were used in the study, with an average initial weight of $360{pm}30.27;kg$. Five animals were used as a control group and were slaughtered at the beginning of the experiment; the remaining animals (n = 25) were distributed in random blocks (repetitions), with body weight as the criterion for block assignment. The animals were fed a diet containing 65% corn silage and 35% of concentrate on dry matter (DM) basis. Five diets consisted of four levels of soybean meal (SM) substituted with CMT (0, 33, 67 and 100%) on a DM basis and a diet with 100% of SM replaced with CMNT. At the end of the experiment, all animals were slaughtered, and their gastrointestinal tracts were emptied to determine their empty body weights (EBW). No significant effects were observed (p>0.05) for the substitution of soybean meal with CMT on intake of dietary nutrients, the average daily body weight gain (ADG) or EBW gain (EBWG). In spite of greater (p<0.05) ricin intake for the diet containing CMNT (3.06 mg/kg BW) compared to the CMT diet (0.10 mg/kg BW/d), there were no effects (p>0.05) on intake of dietary nutrients, ADG or EBWG. The average intake of DM and the ADG were 10,664.63 and 1,353.04 g/d, respectively. Regarding carcass characteristics, only carcass yield in relation to body weight was linearly reduced (p<0.05) upon substitution of SM by CMT. There was no effect (p>0.05) of the substitution of SM by CMT or CMNT on the yield of carcass basic cuts. CMT prices that are higher than 85% of the SM price do not economically justify the use of CMT. For CMT prices between 20 and 80% of the SM price, the optimal level was 67% substitution, while for prices below 15% of the SM price, the optimal level was 100% substitution with CMT. It can be concluded that treated castor meal with 6% lime can totally replace soybean meal in beef cattle diets.