Phytase from a soy sauce koji mould was produced by solid state fermentation using soybean meal as the main substrate. The cultivation was carried out at 30 degrees C for 96 h. Characterization of the crude phytase showed that the maximum activity was obtained when the reaction was carried out at 75 degrees C and pH 5.0. However, after 2-h storage at different pH, maximum remaining activities were obtained when stored at pH 3.6 and 5.5 possibly indicting the presence of two distinct phytase enzymes. However, at different temperatures, there was only one peak of maximum remaining activity after 2-h storage at 40 degrees C. The presence of trypsin and taurochlorate at 1.0% (w/v) did not affect enzyme activity. Digestion of pre-mixed chicken feed with the enzyme koji at approximately 500 U/kg feed in the presence of 1% each of trypsin and taurochlorate increased the phosphate and protein available for animal consumption. (c) 2004 Elsevier Ltd. All rights reserved.