Two　gelatin-hydrolyzing　proteinases　with　molecular　masses　of　85　and　72kDa　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.　©　2011　Wiley　Periodicals,　Inc.