ObjectiveTo study the role of Rac1 in the epithelial-mesenchymal transition (EMT) process of retinal pigment epithelial cells (RPE) induced by transforming growth factorβ(TGF-β). MethodsHuman ARPE-19 cells were divided into 4 groups including control group, TGF-βgroup, TGF-β+NSC23766 group, NSC23766 group. NSC23766 was added to medium 2 hours before TGF-βtreatment to block the Rac1 receptors.α-smooth muscle actin (α-SMA) expression was measured by immunofluorescence and Western blot. Cell scratch assay, invasion assay and gel contraction experiments were used to measure cell migration, invasion, cell contraction. ResultsThe expression ofα-SM A was higher in TGF-βgroup, compared with the control group, TGF-β+NSC23766 group (F=825.314, P < 0.05). Cell scratch assay showed that the cellular gap was less in GF-βgroup, compared with the control group, TGF-β+NSC23766 group, NSC23766 group (F=177.351, P < 0.05). Cell invasion assay showed that, the number of cells pass through the fiber membrane was the same in TGF-βgroup and other 3 groups (F=0.371, P=0.055). Gel contraction assay showed that TGF-βcan promote the cellular contraction, compare to the control group, TGF-β+NSC23766 group, NSC23766 group, the difference was statistically significant (F=40.473, P < 0.05). ConclusionRac1 play a role in TGF-β-induced behavioral changes of RPE cells; NSC23766 inhibit RPE cellular behavior change by regulating Rac1 activation.