A bacterial strain was isolated from homemade Cheongkookjang as a producer of the β-galactosidase, capable of hydrolyzing lactose to liberate galactose and glucose residues. The isolate YB-1105 has been identified as Bacillus licheniformis on the basis of its 16S rDNA sequence, morphology and biochemical properties. β- Galactosidase activity was detected in both the culture supernatant and the cell extract of B. licheniformis YB- 1105. The enzymes of both fractions demonstrated maximum activity for hydrolysis of para-nitrophenyl-β-Dgalactopyranoside (pNP-βGal) under identical reaction conditions of pH 6.5 and 50oC. However, β-galactosidase activity from the culture filtrate was affected more than that from the cell free extract at acidic pHs and high temperatures. The hydrolyzing activity of both β-galactosidases for pNP-βGal was dramatically decreased by the addition of low concentrations of galactose, but was only marginally decreased by high concentrations of glucose or mannose.