Abstract: OBJECTIVE To investigate the effects of curcumin on the metastatic and proliferation ability of human highly metastatic ability lung cancer cell line A549, and explore the role of Rho GTPase in inhibiting lung cancer metastasis by curcumin. METHODS MTT assay was used to determine the effects of curcumin on the proliferation of A549 cells. Invasion assay, and migration assay were used to observe the effects of curcumin on the metastatic ability of A549 cells in vitro. Western blot and RT-PCR were used to observe the effects of curcumin on the expression of RhoA, Rac1, and Cdc42 proteins and mRNA in A549 cells. Laser confocal microscopy was used to investigate the effect of curcumin on the reorganization of the microfilaments marked by immunofluorescent cytochemistry technology. RESULTS Curcumin inhibited the proliferation of A549 cells, and the proliferation inhibition rate increased along with the increase of the concentration and treatment time. When treated with 2.5, 5 μmol·L^-1 for 24 h, the effect of the proliferation inhibition of A549 cells was not significant, but the abilities of invasion and migration of A549 cells were inhibited significantly (P<0.01). In parepell, curcumin significantly suppressed the expression of Rac1, Rac2 and Cdc42 proteins and mRNA (P<0.01). Furthermore, it also influenced the distribution and structure of sytoskeletons. CONCLUSION Curcumin can inhibit the metastatic and proliferation ability of lung cancer cells through down-regulating the expression of Rho GTPase and regulating the cytoskeleton reorganization.