A lactate racemase [EC 5.1.2.1] was isolated and purified about 190 fold in specific activity from the sonic extract of Lactobacillus sake. The purified preparation was almost homogeneous by ultracentrifugal and electrophoretical analyses. Characteristic properties of the enzyme were as follows: (a) absorption spectrum showed a single peak at 274 mμ, (b) molecular weight was 25,000, (c) the enzyme did not require any additional cofactors and showed no activity of lactate dehydrogenase, (d) Km values were 1.7×10-2m and 8.0×10−2m for d- and L-lactate, respectively, (e) optimal pH was 5.8–6.2, (f) an equilibrium point was at a molar ratio of 1/1 (L-isomer/D-isomer), (g) the enzyme activity was inhibited by atebrin, adenosine monosulfate, oxamate and some of Fe-chelating agents, (h) pyruvate and acrylate were not incorporated into lactate during the reaction, and (i) exchange reaction of hydrogen between lactate and water did not occur during the reaction.