Phytase from California Small White beans was extracted, concentrated and enriched by heat treatment and ammonium sulfate fractionation. Crude enzyme fractions tenaciously retained endogenous phytate which could be removed by autolysis at 45°C and pH 5.2. Characterization of the phytase preparation showed: (1) increase in activity with increasing temperature from 37 to 60°C, (2) an activation energy of approximately 9,200 cal/mole for the hydrolysis of inositol hexaphosphate; (3) pH optimum of 5.2; (4) a Kmvalue of 2.22 × 10‐4M; (5) apparently partial inhibition at high substrate concentrations; (6) fully competitive inhibition by one of the reaction products, inorganic phosphate, with Ki=3.1 × 104M. These properties and kinetic constants are comparable to those reported for phytase preparations from similar sources and they adequately account for in situ autolytic loss of phytic acid from these