Acid phosphatase from the yeast <i>Saccharomyces cerevisiae</i> was purified to homogeneity as ascertained by ultracentrifugation and electrophoresis. The purification procedure involved mechanical cell disruption, ethanol precipitation, chromatography on DEAE-cellulose, gel filtration on Sepharose 4B. The sedimentation constant S20<sup>0.580</sup> of the purified enzyme was 15.4 S. Carbohydrate content accounted for 50% of the total molecular weight of the enzyme. The optimum pH for purified enzyme was 3.0-3.5, it was stable at pH 3.0-5.0 at room temperature. After 10 min. incubation at 45° C, 50 per cent of the enzymatic activity was lost. Michaelis constant was found to be 1.3 x 10<sup>-4</sup> M for p-nitrophenylphosphate and 5 x 10<sup>-4</sup> M for 3-glycerophosphate as substrates. The enzyme was inhibited by Hg<sup>2+</sup>, Cu<sup>2+</sup>, Fe<sup>3+</sup>, molybdate, phosphate, arsenate, fluoride ions. Inhibition caused by fluoride ions was noncompetitive, by phosphate - competitive, 5 M urea inactivated the enzyme completely, inactivation was reversible at urea concentration below 2,5 M.