Supplementation of xylanase to pig diets can hydrolyze arabinoxylan (AX) into lower molecular weight compounds and thereby decrease the viscosity and improve nutrient utilization. Xylanase supplementation has, however, shown variable effects in diets containing wheat, rye, and combinations thereof. Differences in animal age, enzyme source and dose, target substrate, and diet processing may explain this. The objective was to study the effect of increasing doses of endo-1,4-β-xylanase from Trichoderma reesei on apparent total tract digestibility (ATTD) of OM, starch, nonstarch polysaccharides (NSP), AX, fat, N, and P of rye fed to growing pigs. Twenty-four 47-kg pigs were assigned to 4 diets containing 97.85% rye and 0, 4,000, 8,000, or 16,000 units xylanase/kg (as-fed basis). Pigs were placed in metabolic cages for 10 d: 5 d for adaption and 5 d for total but separate collection of feces and urine. The ATTD of OM, starch, N, and P did not differ among treatments. The ATTD of total NSP, AX, and fat was, however, higher (P < 0.05) in pigs fed 8,000 units xylanase/kg compared with pigs fed 4,000 and 16,000 units xylanase/kg but not different from pigs fed the control diet without xylanase. The urinary excretion of N and P did not differ among treatments. Besides a linear effect (P = 0.05) on ATTD of fat, there were neither linear nor quadratic responses to xylanase supplementation on ATTD of OM, starch, NSP, AX, fat, N, and P. In conclusion, supplementation of endo-1,4-β-xylanase did not improve the nutritional value of rye in growing pigs.