Bacillus subtilis strain with highly active chitosanase was isolated from the intestine of Sebastiscus marmoratus (scorpion fish). It was named as Bacillus subtilis CH1 by morphological, biochemical and 165 rRNA gene analysis. The optimal conditions for chitosanase production were investigated. The optimum carbon and nitrogen sources for Bacillus stibtilis CH1 were 2% starch and 1% yeast extract respectively. Unlike other chitosanases, the expression of this chitosanase was not induced or slightly induced with chitosan. The chitosanase secreted into the medium were concentrated with ammonium sulfate precipitation and purified by gel permeation chromatography. The molecular weight of purified chitosanase was 30 kDa. The optimum pH and temperature of purified chitosanase were 5.5 and $60^{circ}C$ respectively. The purified chitosanase was continuously thermostable at $40^{circ}C$ and showed stable activity between pH 6.0 and 8.0. Chitosanase activity of Bacillus subtilis CH1 under optimum condition was 4.1 units/ml.