An extracellular protease of Salmonella schottmulleri was purified from culture filtrate by using 0-75% ammonium sulfate precipitation, DEAE Sepharose Fast Flow ion exchange chromatography, Ultrogel HA chromatography and Sephacryl S-200 HR molecular sieve chromatography. To measure enzyme activity, synthetic dipeptide substrate (CBZ-arg-arg-AFC) with low molecular weight was employed as substrate. The molecular weight of the purified enzyme was approximately 80 kDa when determined by gel filtration on Sephacryl S-200 HR and 73 kDa when estimated by SDS-PAGE. The isoelectric point was 5.45. The activity of the purified enzyme was inhibited by metal chelating agesnts such as EDTA and 1.10-phenanthroline. The divalent cations, such as Ca$^$2+/, Zn$^$2+/, Fe$^$2+/, Mg$^$2+/ enhanced its activity. These results suggested that it was a metalloprotease. It had a narrow pH optimum of 6.5-7.5 with a maximum at pH 7.0 and a temperature optimum of 40.deg.C. It was stable at least for 1 week at 40.deg.C and maintained its activity for 24 hours at 50.deg.C, but it was rapidly inactivated at 65.deg.C. This protease was shown to be sensitive to sodium 50.deg.C, but it was rapidly inactivated at 65.deg.C. This protease was shown to be sensitive to sodium 50.deg.C, but it was rapidly inactivated at 65.deg.C. This protease was shown to be sensitive to sodium 50.deg.C, but it was rapidly inactivated at 65.deg.C. This protease was shown to be sensitive to sodium dodecyl sulfate (SDS) and was inactivated in a dose-dependent manner. However, it was resistant to Triton X-100 and the activity was enhanced to 32.3% with treatment of 0.025% Triton X-100.