The DE and ME content (Exp. 1) as well as the apparent ileal digestibility (AID) and standardized ileal digestibility (SID) of essential AA (EAA; Exp. 2) were compared between Chinese corn and U.S. sorghum. The effects of U.S. sorghum as a potential substitute for Chinese corn on growth performance of 114 weaned pigs (8.8 ± 1.0 kg BW; Exp. 3) and 60 growing pigs (23.4 ± 1.6 kg BW; Exp. 4) were evaluated, and the effect of protease supplementation on N utilization was determined in sorghum-based diets fed to growing pigs (Exp. 4). In Exp. 1, there was no difference in DE and ME content between corn and sorghum. In Exp. 2, the AID and SID of most EAA and the concentrations of standardized ileal digestible Lys, Met, Thr, and His were less in sorghum than in corn ( < 0.05). In Exp. 3, there was no difference in ADG and ADFI among treatments during the experimental period. The G:F and apparent total tract digestibility (ATTD) of CP was decreased for pigs fed diets with sorghum in the first 2 wk ( < 0.05) and for pigs fed diets containing 60% sorghum in the following 2 wk ( < 0.05). The fecal score for pigs fed diets with sorghum, regardless of the substitute level, was less ( < 0.05) or tended to be less ( = 0.086) than that for pigs fed diets containing 60% corn. In Exp. 4, no differences were observed in ADG and ADFI overall among pigs fed diets based on corn and soybean meal (CSBM) or sorghum and soybean meal (SSBM). Pigs fed CSBM or SSBM with protease supplementation had greater ( < 0.05) or tended to have greater ( = 0.062) G:F than pigs fed SSBM. Compared with CSBM, SSBM increased fecal N excretion by more than 25% and decreased the ATTD of CP by more than 7% during the whole experiment ( < 0.05). Protease supplementation reduced fecal N excretion by more than 12% and increased ATTD of CP by more than 6% ( < 0.05). In conclusion, based on optimal G:F and CP digestibility, diets for weaned pigs should contain less than 20% sorghum during the first 2 wk and no more than 40% during the subsequent 2 wk after weaning. Sorghum used as an alternative energy source for corn in diets fed to growing pigs decreases CP utilization by increasing manure N output, which might be partially offset by protease supplementation.