AIM:ToinvestigatetheroleofMALAT1incolorectalcancermetastasis.METHODS:ThemRNA expression levels of MALAT1 and Rac1b in the tumor and adjacent normal tissues were examined by real-time PCR. MALAT1 was knocked down by siRNA in colorectal cancer cell lines .The expression of Rac1b and the epithelial-mesen-chymal transition markers was examined by Western blot .Cell proliferation was determined by EdU analysis .The effects of MALAT1 on the cell migration and invasion were examined by Transwell assay .RESULTS: The expression of MALAT1 was down-regulated in colorectal cancer .Down-regulation of MALAT1 induced Rac1b overexpression, which in turn in-creased the expression levels of E-cadherin and β-catenin.Furthermore, down-regulation of MALAT1 promoted the cell proliferation, invasion and migration.CONCLUSION:MALAT1 is associated with metastasis of colorectal cancer through regulating the expression of Rac1b and the downstream factors.