Aminopeptidase　H　(APH)　is　a　universally　distributed　aminoendopeptidase　in　the　tissue　of　many　organisms.　However,　it　is　hard　to　investigate　its　mechanism　underlying　the　catalysis　and　the　function　in　cell.　In　this　article,　the　full　DNA　sequence　of　this　enzyme　was　cloned　from　chicken　liver,　then　subcloned　to　the　vector　pET22　b(+).　The　recombined　vector　was　transformed　into　E.　coli　Rosetta　(DE3),　and　the　APH　gene　was　expressed　by　the　induction　of　IPTG.　It　was　found　that　the　recombinant　protein　exhibited　the　same　molecular　weight　as　authentic　APH　on　SDS-PAGE　analysis;　the　expression　level　increased　with　induction　time　and　approached　maximum　of　94.7　mg/L　till　6　hours,　which　contained　16.7%　of　the　total　protein.　Moreover,　this　recombinant　protein　showed　similar　properties　of　subunit　composition,　thermal　stability　and　optimum　pH　with　native　APH,　based　on　the　enzymatic　assay,　purification　and　analysis　of　enzymological　properties.　Therefore,　it　is　confirmed　that　APH　was　expressed　in　this　prokaryote　system　with　a　high-level　of　1636　u/L　aminopeptidase　activity.　These　results　would　help　to　elucidate　the　catalysis　mechanism　and　biological　function　of　APH　by　providing　enough　material.　©　2008　Institute　of　Microbiology,　Chinese　Academy　of　Sciences　and　Chinese　Society　for　Microbiology.