This experiment was conducted to determine the effects of supplementing diets with cellulase on the nutrient digestibility of the diets and on the performance of pigs (starter, grower, and finisher). Twenty-eight (28) individually penned crossbred pigs with about 23 kg live weights were randomly distributed to four dietary treatments following a completely randomized design. The four treatments were basal and reduced ME starter, grower, and finisher diets supplemented with 0.05% and 0.10% cellulase. Reduction of ME of grower and finislrer diets did not affect the apparent digestibility (aCOD) of crude fiber. Supplementation of reduced ME grower and finisher diets with 0.05 to 0.10% cellulase did not significantly affect the aCOD of crude fiber, crude fat, and nitrogen-free extract. Reduction of ME of starter, grower, and finisher diets did not significantly influence the ADG, ADFC, FCR, and feeding period in all phases of growth. Cellulase supplementation of reduced ME diets likewise did not significantly affect all the parameters considered. Carcass recovery, loin eye area and backfat thickness did not significantly differ among treatments. Income over feed cost decreased consistently with higher level of cellulose supplementation of the reduced starter, grower and finisher diets.