Plasma　kallikrein　(PK),　a　serine　protease　in　the　trypsin　clan　(SA),　plays　critical　roles　in　many　physiological　and　pathological　pathways.　Regulating　the　abnormal　activity　of　PK　has　been　successfully　used　in　the　clinical　therapy　of　hereditary　angioedema.　In　this　study,　the　serine　protease　domain　of　murine　plasma　kallikrein　(mPK)　was　expressed　in　the　pichia　pastoris　system.　The　recombinant　protein　was　a　glycosylated　active　enzyme　after　purification　by　the　cation　exchange　and　size-exclusion　chromatography,　and　was　crystallized　at　the　precipitant　condition　of　25%　PEG　3350,　0.1　M　Tris-HCl　pH　8.5　and　0.1　M　NaCl.　The　crystal　structure　of　mPK　was　determined　at　2.6　angstrom.　This　is　the　first　published　crystal　structure　of　mPK,　showing　some　distinctive　features　at　S2＇　and　S3＇　pockets　when　compared　to　its　human　analogue　(human　plasma　kallikrein,　hPK).　In　addition,　mPK　show　unique　structural　features　in　the　non-conservative　67-72　and　76-81　loops　when　compared　to　other　serine　proteases.　These　results　provide　insights　for　the　design　of　potent　and　selective　PK　inhibitors.