The requirement for Cu for normal metabolism by weanling pigs is 5 to 6 mg/kg, but it is common practice to include additional Cu in diets for pigs to enhance growth performance. Several modes of action for the improved growth performance have been proposed, and one proposed mode of action is the ability of Cu to alter microbial activity. The apparent total tract digestibility (ATTD) of acid hydrolyzed ether extract (AEE) is improved if Cu hydroxychloride is supplemented to high fiber diets. Therefore, an experiment was conducted to test the hypothesis that inclusion of 150 mg/kg of Cu from Cu hydroxychloride (IntelliBond C^II; Micronutrients USA LLC; Indianapolis, IN) to diets fed to growing pigs improves apparent ileal digestibility (AID) and ATTD of AEE, and the AID of crude protein. The second objective was to test the hypothesis that supplementing diets with Cu hydroxychloride can reduce the concentration of microbial protein in the small intestine or in the large intestine by pigs fed a corn-soybean meal diet or a diet based on corn, soybean meal, and distillers dried grains with solubles (DDGS).