B.subtilis 05 expressing highly β-mannanase was isolated from pond sludge.And the enzyme characteristic had been determined.The results showed that optimum temperature was 50℃,the activity kept stable during 4-45℃,optimum pH was pH8.0 for the reaction,the Na+,K+ promoted significantly the activity,and the(NH4)-slightly inhibited,the Mg2+,Cu2+,Fe2+ inhibited significantly,the Fe3+ inhibited activity very significantly.The viscosity of fermentation medium was 2.78 Poise after cultivation of 10.5 hours.The viscosity reached 1.55 Poise after cultivation of 12 hours.