Abstract: A strain of Bacillus pumilus,Van35,was isolated and screened from the surface of flue-cured tobacco leaves,the microbial agent prepared from it was sprayed on cut tobacco.The treated cut tobacco was fermented at 45℃ and relative humidity 60% for 21 days.The contents of total sugar,reducing sugar,K,cellulose,protein,total nitrogen and nicotine in treated cut tobacco were determined,the results showed that the contents of total sugar,reducing sugar and K in the treated tobacco increased,while those of cellulose,protein,total nitrogen and nicotine decreased somewhat;the ratios of sugar to nitrogen,sugar to nicotine and nitrogen to nicotine raised to some extent,and the chemical compositions in tobacco became more harmonious.It indicated that Van35 treatment could enhance tobacco flavor,mellow tobacco smoke,reduce irritation,mask offensive odor and improve smoking taste obviously.