Abstract: Objective 　To evaluate the effect s of the arsenic t rioxide (As2O3 ) on antagonizing invasion and metastasis and to investigate the effect of As2 O3 on RhoC gene expression in Human Hepatocarcinoma cell line Hep G2. Methods 　Adherence ability, Migration and invasion of Hep G2 cell inhibited by As2 O3 were assessed by MTT and t ranswell technique. Expression levels of RhoC2mRNA and protein in Hep G2 cell were determined by reverse t ranscription2polymerase chain reaction ( RT2PCR) and Western blot, re2 spectively. Results 　The number of adhesion, migration and invasion of Hep G2 cells were significantly lower in As2O3 Group than in the cont rol group ( P < 0. 05) . A significant down - regulation of expression of RhoC gene mRNA and protein levels were observed in Hep G2 cells when 0. 25 mg/ L As2O3 was given af ter 4, 6 and 8 days ( P < 0. 05) . Relations between mRNA and protein expression level of RhoC gene in Hep G2 were found close ( rA = 0. 92, P = 0. 046) . Conclusion 　The adherence, migration and invasion abil2 ity of Hep G2 cell is markedly inhibited by As2O3 . As2O3 is able to inhibit the invasion and metastasis of Hep G2 cells by down2regulation of RhoC gene expression.