Abstract: In order to screen a high extracellular β-glucosidase producing mutant strain of Saccharomycaes cerevisiae, the method of UV mutation was used on wild yeast of MQFSM- 3. Death rate affected by UV mutagenesis conditions were determined,enzyme activity and enzymatic characteristics of mutant strain were also evaluated. The results showed that the dose of 3500 μJ/cm2,irradiation 9 min,mortality reached 81.09%.By preliminary screening,rescreening and subculturing for many times,a stable enzyme production of mutant UV- 45 was obtained. Compared with the original strain, its enzyme activity was improved 41. 64 %. The enzymatic characteristics were analyzed that the optimum temperature of UV-45 was 50 ℃,and it had a good thermal stability between 20⁵0 ℃. The optimum p H was 5.5,and between p H4.0 to 6.5,the enzyme activity was relatively stable.