Two studies were conducted to determine the effects of cereal type (corn v. wheat) and xylanase supplementation (with vs. without) on energy digestibility and growing pig performance. In Exp. 1, 440 pigs (initial BW 7.8 ± 2.4 kg) were randomly allotted to 1 of 4 dietary treatments and used in a 28-d growth study. No significant cereal x enzyme interactions or main effects of cereal and enzyme were observed for any of the growth criteria evaluated (P > 0.84). In Exp. 2, 72 pigs from Exp. 1 were used in a metabolism study. Pigs remained on the same dietary treatment as in Exp. 1. Feces were collected, and apparent total tract digestibility (ATTD) of dry matter (DM) and gross energy (GE) were determined. A cereal × xylanase interaction was observed (P < 0.0001) for ATTD of DM and GE due to xylanase supplementation improving both ATTD of DM and GE in corn-based diets (85.6 v 87.6 % and 85.4 v 87.4 %, respectively), but decreasing ATTD of DM and GE in wheat-based diets (89.3 v 86.3 % and 89.7 v 86.6 %, respectively). Thus, the effects of xylanase supplementation on DM and GE digestibility may depend on cereal type, and increases in DM and GE may be observed when xylanase is added to corn based diets.