In the present work, caseinase was extracted from a municipal solid waste (MSW) compost after 5 h of agitation using 0.05 M sodium pyrophosphate at pH 9. The extract was ultrafiltered. The resulting fraction was called UF 2 (F < 0.45 μm, molecular weight > 10,000 Da). After precipitation on a gradient of ammonium sulfate, the enzymatic solution was characterized and compared with a commercial neutral protease (from Bacillus polymyxa,). The extracted enzyme was less susceptible to thermal denaturation or autodigestion during storage than the commercial protease. A possible association with soluble organic matter present in the compost may have stabilized the enzyme, similar to stabilization of soil enzymes. The action of these stabilized enzymes may have great importance in the mineralization of proteins and their use as available sources of nitrogen for microorganisms in composting or after soil addition.