A bacterial strain capable of producing a thermo-acido-tolerant phytase was isolated from soil around haystacks and designated as strain PH01 The phytase produced was purified to homogeneity as determined by native PAGE. From SDS-PAGE, it was 30 kDa in size. The purified phytase was a thermo-acido-tolerant enzyme. A complex medium for the PH01 phytase production was developed. The medium, "PheB", was composed of 2% glucose, 0.2% CaCl2, 0.5% NH4NO3, 0.05% KCl, 0.05% MgSO4 . 7H(2)O, 0.001% FeSO4 . 7H(2)O, 0.001% MnSO4 . H2O in rice bran plus soybean meal extract containing 3% (v/v) phosphate solution (7.3% NaHPO4 + 3.2% KH2PO4, pH 7.2). Cultivation was done at 37 degreesC with aeration for 48 h which produced phytase at 10 U/ml. Exposure of the phytase to 1% bile salt; i.e., taurocholate or deoxycholate, caused less than 15% reduction of activity. Potential application of PH01 phytase as a feed supplement was suggested.