A keratinolytic protease-producing microorganism was isolated from soybean paste waste and was identified as a strain of Bacillus sp. The keratinase was purified by polyethylene glycol precipitation and two successive column chromatographies with DEAE-Toyopearl 650C and Sephacryl S-200 HR. The purified enzyme had overall 11 purification folds with an 18% yield. The results of sodium dodecyl sulfate polyacrylamide gel electrophoresis and gel filtration on Sephacryl G-200 indicated that the purified enzyme was monomeric and had a molecular weight of 134 kDa. The optimum temperature and pH were 40 degrees C and 7.0, respectively. This enzyme was completely inhibited by EDTA and EGTA, and it was restored by the addition of Ca2+ and Mg2+. These results suggested that it is a metalloprotease. The stimulated enzyme activity by reducing agents indicated that the reducing condition was important in the expression of the activity.