Arginase (ARG) is a kind of inducible manganese (Mn2 )-containing enzymes that catalyse?the?final?step?of?the?urea?cycle?in?the?liver,?converting?l?-arginine?into?l?-ornithine and urea.Therefore, we can measure its bioactivity by enzyme activity assay. Recombinant human Arg was diluted to different concentrations in deionized water.Loading 40 μL of the rhARG1 and 10ul Substrate mixture(100 mM Arginine, 500 mM Glycine, 1.25?mM?MnCl2, pH 10.5 ) into the plate. Incubated at 37 °C for 2 hours and stop the reaction with 200 μL stop solution of the 2 mM oPA, 2 mM NED ,50 mM Boric Acid, 1 M Sulfuric Acid, 0.03% Brij-35 (w/v) .Cover the plate and incubate at room temperature for 20 minutes and read at 520 nm (absorbance) in endpoint mode. The specific activity of recombinant human ARG is >24400pmol/min/ug.