Abstract: The spores of Bacillus megatherium(B_CK) from tobacco leaf surface were mutagenized physically and chemically.From the plates with soluble starch and casein mediums,the strains with higher Hc value(the diameter ratio of clearing ring and colony) were selected.The selected strains were repeatedly screened by shaking along with measuring α-amylase and protease activities in fermentative liquid,strain B₈ of higher activity was obtained,whose α-amylase and protease activities were 1.964 and 2.266 times of that of B_CK,respectively.The strain has a good genetic stability after 5-generation subculture,its α-amylase and protease activities stabilized within the ranges of 2.821-3.273 U/mL and 21.21-27.36 U/mL,respectively.