The phosphatase of a psychrophile was purified by ammonium sulfate fractionation, and a sequence of chromatographies on DEAE-Cellulofine, butyl-Cellulofine, Sephacryl S-100, and Mono-Q columns. The purified enzyme preparation was found to be electrophoretically homogeneous on native- and SDS-PAGE, and its molecular mass was determined to be 38.4 kDa by MALDI-TOF mass spectrometry. Maximal activity was observed at 30 degrees C and pH 6.0. Furthermore, the activity of this enzyme at 0 and 5 degrees C was 27 and 28%, respectively, of that at 30 degrees C. The enzyme was stable in the pH range of 6.0 to 8.0 and up to 20 degrees C. The enzyme was affected by metal ions; the activity was enhanced by Mg2+ and Ca2+ ions, but depressed by Zn2+ ions. Analysis of the amino acid composition indicated that this phosphatase contains no S-S bond, and only a few prolyl residues necessary to retain the rigid structure of a protein molecule. The phosphatase shows typical features of a cold enzyme; high catalytic activity at low temperature and rapid inactivation at an intermediate temperature.