Human liver alkaline phosphatase (E. C. 3. 1. 3. 1) has been purified by butanol extraction, acetone precipitation, and a combination of diethylaminoethyl (DEAE)-cellulose, carboxymethyl (CM)-cellulose, Sephadex G-200 gel chromatography. The homogeneity of purified enzyme was demonstrated by disc electrophoresis and micro-Ouchterlony. The heat activation for hydrolysis of p-nitrophenyl phosphate was calculated as 21000 cal/mole and liver alkaline phosphatase was inhibited by homoarginine. A molecular weight of 180000 was obtained by gel filtration and isoelectric point of pI 4.7 was determined by isoelectric focusing. The optimum pH for the hydrolysis of p-nitrophenyl phosphate was 10.6 and optimum temperature was 40°in the standard assay system and other enzyme properties were also examined.