AIM: To investigate the damaging effect of high-intensity focused ultrasound (HIFU) on cancer cells and the inhibitory effect on tumor growth. METHODS: Murine H22 hepatic cancer cells were treated with HIFU at the same intensity for different lengths of time and at different intensities for the same length of time in vitro, the dead cancer cells were determined by trypan blue staining. Two groups of cancer cells treated with HIFU at the lowest and highest intensity were inoculated into mice. Tumor masses were removed and weighed after 2 wk, tumor growth in each group was confirmed pathologically. RESULTS: The death rate of cancer cells treated with HIFU at 1 000 W/cm2 for 0.5, 1, 2, 4, 8, and 12 s was 3.11±1.21%, 13.37±2.56%, 38.84±3.68%, 47.22±5.76%, 87.55±7.32%, and 94.33±8.11%, respectively. A positive relationship between the death rates of cancer cells and the length of HIFU treatment time was found (r=0.96, P<0.01). The death rate of cancer cells treated with HIFU at the intensity of 100,200,400,600,800, and 1 000 W/cm2 for 8 s was 26.31±3.26%, 31.00±3.87%, 41.97±5.86%, 72.23±8.12%, 94.90±8.67%, and 99.30±9.18%, respectively. A positive relationship between the death rates of cancer cells and the intensities of HIFU treatment was confirmed (r= 0.98, P<0.01). The cancer cells treated with HIFU at 1 000 W/cm2 for 8 s were inoculated into mice ex vivo. The tumor inhibitory rate was 90.35% compared to the control (P<0.01). In the experimental group inoculated with the cancer cells treated with HIFU at 1 000 W/cm2 for 0.5 s, the tumor inhibitory rate was 22.9% (P<0.01). By pathological examination, tumor growth was confirmed in 8 out of 14 mice (57.14%, 8/14) inoculated with the cancer cells treated with HIFU at 1 000 W/cm2 for 8 s, which was significantly lower than that in the control (100%, 15/15, P<0.05). CONCLUSION: HIFU is effective on killing or damage of H22 hepatic cancer cells in vitro and on inhibiting tumor growth in mice ex vivo. A: To investigate the damaging effect of high-intensity focused ultrasound (HIFU) on cancer cells and the inhibitory effect on tumor growth. METHODS: Murine H22 hepatic cancer cells were treated with HIFU at the same intensity for different lengths of time and at different intensities for the same length of time in vitro, the dead cancer cells were determined by trypan blue staining. Two groups of cancer cells were treated with HIFU at the lowest and highest intensity were inoculated into mice. Tumor masses were removed and weighed after 2 weeks, RESULTS: The death rate of cancer cells treated with HIFU at 1 000 W / cm2 for 0.5, 1, 2, 4, 8, and 12 s was 3.11 ± 1.21%, 13.37 ± 2.56% , 38.84 ± 3.68%, 47.22 ± 5.76%, 87.55 ± 7.32%, and 94.33 ± 8.11%, respectively. A positive relationship between the death rates of cancer cells and the length of HIFU treatment time was found (r = 0.96, P < 0.01). The death rate of cancer cells treated with HIFU at the in Tensity of 100, 200, 400, 600, 800, and 1 000 W / cm2 for 8 s was 26.31 ± 3.26%, 31.00 ± 3.87%, 41.97 ± 5.86%, 72.23 ± 8.12%, 94.90 ± 8.67%, and 99.30 ± 9.18%, respectively. between the death rates of cancer cells and the intensities of HIFU treatment was confirmed (r = 0.98, P <0.01). The cancer cells treated with HIFU at 1 000 W / cm2 for 8 s were inoculated into mice ex vivo. The tumor inhibitory rate was 90.35% compared to the control (P <0.01). In the experimental group inoculated with the cancer cells treated with HIFU at 1 000 W / cm2 for 0.5 s, the tumor inhibitory rate was 22.9% (P <0.01). By pathological examination, tumor growth was confirmed in 8 out of 14 mice (57.14%, 8/14) inoculated with the cancer cells treated with HIFU at 1 000 W / cm2 for 8 s, which was significantly lower than that in the control (100 %, 15/15, P <0.05) CONCLUSION: HIFU is effective on killing or damage of H22 hepatic cancer cells in vitro and on inhibiting tumor growth in mice ex vivo.