Abstract: The objective of this study was to purify β-mannase from Bacillus subtilis WD-23 and examine its enzymology properties. This study used the combining methods of ammonium sulfate, semi-permeable membrane dialysis, polyethylene glycol concentration, DEAE-Sepharose FF ion exchange chromatography, Sephadex G-75 gel filtration and SDS-PAGE gel electrophoresis to purify β-mannase. The result showed that the purified ratio of β-mannase of B. subtilis WD-23 was 14.1 by using the above methods, and the molecular mass was about 40 ku, the optimal pH and the stability range of pH were 5.6 and 5.0-7.0 respectively, and optimal temperature and the stability range of temperature were 55 ℃ and 40-70 ℃ separately, Ca^{2 +} was the most obvious effect on the activation of the enzyme, on the contrary, the inhibitory effect of Li⁺ was the most obvious.