A bacteria strain producing extracellular $eta$-mannanase was isolated from soil and was identified as Bacillus subtilis by 16S rRNA sequence comparison and biochemical determinations. The optimum pH and temperature for the $eta$-mannanase activity were 5.0 and 5.5$^{circ}C$, respectively. The zymogram technique revealed a single protein band exhibiting $eta$-mannanase activity from the culture supernatant. The molecular mass of the enzyme was estimated at approximately 130 kDa. The addition of 0.5% lactose or 0.5% locust bean gum to the LB medium caused to Increase significantly the $eta$-mannanase productivity from Bacillus subtilis JS-1. The cells grown on LB medium supplemented with lactose produced maximal enzyme activity at the stationary phase. In contrast to this, the $eta$-mannanase was induced at the logarithmic phase from the cells grown on LB medium supplemented with locust bean gum. The discrepancy in induction times suggests that $eta$-mannanase was induced by different induction mechanisms depending on the carbon sources in Bacillus subtilis JS-1 .