Among various tissue-specific alkaline phosphatases, sialic acid was detected in liver, placental and meconial alkaline phosphatases, but not in the intestinal one. The content of acidic amino acids was larger than that of basic amino acids in the purified enzymes. Placental, intestinal and liver alkaline phosphatases contained 4 g-atoms of zinc/mol of enzyme, but the meconial alkaline phosphatase contained 2 g-atoms of zinc / mol of enzyme. N-Terminal amino acid residues of the intestinal and meconical alkaline phosphatases were both phenylalanine, whereas that of placental enzyme was isoleucine and that of liver enzyme was leucine. The tryptic peptide patterns of human placental, intestinal, meconial and liver alkaline phosphatases were similar to one another in part. The activecenter-containing peptides labelled with ³³PO₄ from human placental, intestinal, meconial and liver alkaline phosphatases had the same mobility on a thin layer chromatogram.