An experiment was conducted to test the hypothesis that the apparent total tract digestibility (ATTD) and the standardized total tract digestibility (STTD) of phosphorus in fermented soybean meal (FSBM) are greater than conventional soybean meal when fed to growing pigs. Four diets were formulated to contain conventional SBM or FSBM and either 0 or 800 units/kg of microbial phytase. The only sources of phosphorus in these diets were the soybean meals. A phosphorus-free diet to estimate basal endogenous losses of P was also formulated. Thirty barrows weighing about 14kg were placed in metabolism cages and allotted to five diets in a randomized complete block design with six pigs per diet. Feces were collected for five days after a five-day adaptation period. All samples of ingredients, diets, and feces were analyzed for phosphorus and values for ATTD and STTD of phosphorus were calculated. Results indicated that the basal endogenous phosphorus losses were 187 mg/kg dry matter intake. As phytase was added to the diet, the ATTD and STTD of phosphorus increased (P < 0.01) from 60.9 to 67.5% and from 65.5 to 71.9%, respectively, in pigs fed FSMB. Likewise, addition of phytase to conventional soybean meal increased (P < 0.01) the ATTD and STTD of phosphorus from 41.6 to 66.2% and from 46.1 to 71.4%, respectively. The ATTD and STTD of phosphorus were greater (P < 0.01) in FSBM than in conventional soybean meal when no phytase was used, but that was not observed when phytase was added to the diet (soybean meal × phytase interaction, P < 0.01). In conclusion, the ATTD and STTD of phosphorus in FSBM was greater than the conventional soybean meal when no microbial phytase was added, but, when phytase was added to the diets, no differences in phosphorus digestibilities were observed.