Endo-1,4-v-mannanase was purified to homogeneity from the culture supernatant of Bacillus subtilis KU-1 by ammonium sulfate precipitation, DEAE-Toyopearl, phenyl-Sepharose and FPLC Mono Q column chromatography by 810-fold with 39% yield. The molecular mass of the enzyme was estimated to be 39 kDa by SDS-PAGE and 40 kDa by gel filtration. It had a pI of 4.5 with maximum activity at pH 7.0 and 50^553C. It was stable for 48 h between pH 4.5 and 9.0, and for 1 h up to 603C. The enzyme activity was strongly inhibited by Hg2