Abstract: In the present work.MCF-7 cells mixed with polyethylenimine:Deoxyribonucleic acid(DNA) complex and microbubbles were exposed to 1 MHz ultrasound with low acoustic driving pressures(0.05 ~ 0.3 MPa).The sonoporation pores generated on the cell membrane were examined with scanning electron microscopy.The results show that larger sonoporation pores would be generated with the increasing acoustic pressure or longer treatment time,which could be useful for the enhancement of DNA transfection efficiency,the mean diameters of pores ranged from 100 nm to 1.25μm. The calculated results based on Marmottant model indicate that the microstreaming-induced shear stress might be involved in the mechanisms of the low-intensity ultrasound induced sonoporation.