1. A strain of Bacillus cereus was isolated from the soil which produced an enzyme acting on water-soluble Lea substance and group OLe (a+b-) red cells. The enzyme preparation also contains A-decomposing enzyme, but not O(H) -, Leb-and B-decomposing enzymes. Decomposition of Lea activity of Lea substance and Le (a + b-) red cells with this enzyme resulted in the enhancement of the cross-reactivity of Lea substance and Le (a+b-) red cells with anti-pneumococci Type XIV chicken serum.2. These enzymes were found in a fraction which precipitated at 30-60% ammonium sulfate saturation of bacterial autolysate. By means of DEAE cellulose column chromatography, the Lea-decomposing enzyme could be separated from the A-decomposing enzyme. The optimal pH of these enzyme action ranged 6.8-7.2, the optimal temperature 30-37°C and the enzymes were inactivated by heating at 70°C for 5 minutes.3. The action of these enzymes were inhibited by such metal salts as copper sulfate, mercuric chloride and strontium nitrate. The enzyme action to decompose Lea substance was inhibited strongly by L-fucose, D-galactose and lactose, and slightly by β-ethyl-N-acetyl-D-glucosaminide and D-glucosamine. The results of the inhibition of enzyme action by sugars indicate that the structure of L-fucose and β-linked D-galactose combined with β-D-N-acetylglucosamine is important as antigenic determinant of Lea specificity. The action of A-decomposing enzyme was inhibited strongly by N-acetyl-D-galactosamine and slightly by D-galactosamine.