In this study,the effect of low intensity ultrasonic irradiation treatment on Saccharomyces cerevisiae (S.cerevisiae) were evaluated by the biomass increment under the different conditions of growth phase,ultrasonic frequency,ultrasonic power intensity and processing time.Then research the S.cerevisiae cell membrane permeability and ethanol tolerance after treating by low intensity ultrasound.The results showed that the optimum ultrasonic treatment conditions for the maximum biomass increment of Saccharomyces cerevisiae as follows: 28 KHz ultrasound irradiation with power intensity 140 W/L,S.cerevisiae culture at late stagnant phase,and treating for 1 h.Under these conditions,the S.cerevisiae biomass increment reached to 127.03%.In addition,the content of extracellular protein,nucleic acid and Fructose-l,6-diphosphate (FDP) were increased on S.cerevisiae under the optimal ultrasonic condition,these means the cell membrane permeability became stronger,and the ethanol tolerance of S.cerevisiae was not affected compared with control group.