An experiment was conducted to evaluate effects of dietary supplementation of a corn-or a wheat-based diet with two sources of exogenous xylanase (fungal or bacterial originated) on productive performance, ileal nutrients digestibility, nitrogen-corrected apparent metabolisable energy (AME n ) and digestive organs morphometry in broiler chickens. Broilers were fed with one of the six dietary treatments consisting of two basal diets (based on corn or wheat) each with or without xylanase (from bacterial or fungal origin) supplementation. Compared with corn-based diet, feeding birds with the wheat-based diet improved weight gain and feed intake by 4.71 and 4.81%, respectively, and ileal digestibility of dry matter and crude protein were greater in birds fed wheat-based diets compared with the birds grown on corn-based during Days 1-21 of age (p<.05). Villus length and villus length to crypt depth ratio increased (p < .05) in birds received wheat-based diets compared with those fed on corn-based diets. Gizzard weight was greater in birds fed with corn-based diets on days 21 and 42 of age by 11.5% and 31.8%, respectively, compared with those received wheat-based diets (p < .05). Supplementing diets with fungal xylanase increased liver weight in birds grown on wheat-based diets compared with those grown on control and corn-based diets, respectively, on Days 21 and 42 of age (p < .05). It was concluded that supplementing a corn-or wheat-based diet with a xylanase of bacterial or fungal origin had no effect on productive performance or AMEn of diets in broiler chickens during the starter and growing periods. ARTICLE HISTORY