A bacterium producing the extracellular mannanase was isolated from Korean formented food and has been identified as a member of the genus Bacillus from the result of the phylogenic analysis based on partial 165 rRNA sequences. The isolate, named Bacillus sp. WL-3, was shown to be similar to B. subtilis strain on the basis of its biochemical properties. The mannanase of culture supematant was the most active at $55^{circ}C$ and pH 6.0. The additional carbohydrates including u-cellulose, avicel, oat spelt xylan, guar gum and locust bean gum (LBG) increased the mannanase productivity. Especially, the maximum mannanase productivity was reached 65.5 U/ml in LB medium supplemented with 0.5% (w/v) LBG, which was 131-folds more than that in LB medium. It was sug-gested that the increase of mannanase production was owing to induction of mannanase biosynthesis by LBG hydrolysates transported following initial hydrolysis by extracellular mannanase during the cell growth. The molec-ular weight of WL-3 mannanase was estimated to approximately 38.0 kDa by zymogram on SDS-PAGE.