Abstract: To investigate the effect of ultrasound irradiation on viability of HepG₂ cells in vitro,the parameters of acoustic intensity,duty factor and duration of therapeutic ultrasound are selected,and the ultrasound irradiations are performed according to the orthogonal design.After 24 h of ultrasound irradiations,MTT assays are performed to assess the viability of HepG₂ cells.The morphologic change of cells are observed using optical micrography before and after ultrasound irradiation.The results show that,when the acoustic intensity is greater than 2 W/cm² with any duty factor or the acoustic intensity is 1.5 W/cm² with the duty factor greater than 60%,the viability of HepG₂ cells decreases significantly,and the detachment,craterlike aggregation,and cell fragmentation of cells could be observed by optical microscope.When the acoustic intensity ranges from 0.5 to 1.0 W/cm² and the duty factor is 10%-20%,the rate of cell viability can be more than 90% immovably.The statistical analysis of orthogonal design indicates that the acoustic intensity and duty factor are the most important parameters for the HepG₂ cell viability irradiated by therapeutic ultrasound in vitro.