Abstract: Alkaline phosphatase(AKP)was purified from the liver of Leiocassis longirostris by a biochemical method.The purification multiple was 6 2.0 8 and the specificactivity was 66.43 unit/mg protein,In PAGE and SDS-PAGE,the liver of Leiocassis longirostris AKP formed a single band.The optimum pH for the enzyme was pH10.05;when 7.0pH11,it was uhstable. The optimum temperature was about 40℃,it was unstable against heat.The Km value was 1.82×10-3mol/L with disodium phenyl phosphate as its substrate. The activator of the enzyme was Mg2+,while inhibitors were KH2PO4,L-Cys,ME,DFP,and EDTA-Na2,KH2PO4 and DFP were selected for determining the types of inhibhion and the results showedthat KH2PO4 was a competitive inhibitor with the inhibition constant being 2.41mmol/L,and that DFP was a noncompetitive inhibitor with the inhibition constantbeing 1.01m mol/L.