Abstract: The strain B19 with high yield of β- mannosidase was isolated from forest soil sample using first screening( Konjac powder as the sole carbon source and Congo red staining method) and secondary screening( determination of β-mannosidase enzyme activity by p-Nitrophenyl-β-D-Mannopyranoside method).The strain was identified as Enterobacter sp. by electron microscopy,Gram- staining,physiological and biochemical examination,16 S r DNA sequence and phylogenetic tree analysis. The strain B19 could produce intracellularβ- mannosidase,and its activity could be up to 1.26 U / m L when the strain was cultivated 48 h under the condition of 37 ℃,200 r / min.The enzymatic properties analysis showed that the optimal p H and temperature of this enzyme were 7.5 and 50 ℃,respectively.The enzyme exhibited high thermal stability when the temperature ranged from 45 to 50 ℃,or the p H value ranged from 6.0 to 8.0. The enzyme activity was activated by Mg2 +and Mn2 +in concentration of 10 mmol / L,but was inhibited by K+,Fe2 +,Ca2 +,Cu2 +,Co2 +and Zn2 +. It might be a good candidate strain in studying β- mannosidase.