Two gelatin-hydrolyzing proteinases with molecular masses of 85 and 72 kDa in the sarcoplasmic fraction of grass carp muscle were detected using gelatin zymography. The gelatinolytic activity in dark muscle was obviously higher than that in white muscle. Optimum pH and temperature of the two enzymes were around 8.0 and 40C. The proteinase inhibitor leupeptin entirely inhibited GP-I, but E-64 did not inhibit it. Only EDTA completely suppressed GP-II, and Ca2+ is essential for the activity of GP-II. All these facts indicated that GP-I was matrix serine proteinase, and GP-II was matrix metalloproteinase. When grass carp muscle was stored for 15 days at 4C, GP-I and GP-II were detected during the whole stored period. Therefore, the two gelatinolytic proteinases may be proposed to participate in the tenderization of fish muscle during postmortem stage.