This study was carried out to evaluate the effects of adding phytase on growth performance, nutrient digetibility and phosphoms excretion in weaning-growing pigs fed com-wheat-soy diets. A control diet (C) was formulated with 100% of the NRC P requirement, while a low P diet at 80% of the NRC P requirement (B), a low P diet with 500 FTU (One unit of phytase (=FTU) is defined as the quantity of enzyme which liberates 1 micromol of inorganic phosphoms per minute from 0.0015 ㏖/ℓ sodium phytate at pH 5.5 and 37℃) of phytase (BPS) and a low P diet with 1,000 FTU of phytate (BP10) were fed to the other groups. Average daily gain of pigs fed the C diet was higher than that of pigs fed the B diet, but was similar to that of pigs fed the BPS and BPIO diets. There were no significant differences in feed intake among treatments. Feed/gain ratio of pigs fed the C diet was better than that of pigs fed the B diet (P$lt;0.05), but feed/gain ratios of pigs fed the BPS and BP10 diet were similar to that of pigs fed the C diet. No significant differences were found among treatments in nutrient digestibilities during the weaning phase. In the growing phase, digestibility of dry matter, crude protein and crude fat of the B diet were lower than that of the C diet. Adding phytase to the B diet improved the nutrient digestion coefficient (P$lt;0.05). Phosphoms digestibility of the C diet was lower than those of the B, BPS and BP10 diets. Dry matter and protein excretion in pigs fed the B diet were higher than control pigs (P$lt;0.05). Adding phytase at the level of 500 FTU to the B diet resulted in no significant change in nutrient excretion. However, adding 1,000 FTU phytase to diets of weaning-growing pigs reduced nutrient excretion considerably.