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The epithelial-mesenchymal transition (EMT) plays a critical role in cancer progression, metastasis and drug resistance. The transcription factor(TF) and microRNA (miR) chimeric [SNAIL/miR-34]:[ZEB/miR-200] unit is the core regulatory system for the EMT process. Here, we proposed to assess the anti-EMT abilities and explore the inherent pharmacological mechanisms of the classic hypoglycaemic agent metformin for colorectal cancer(CRC).For the EMT model, the TGF-β-induced CRC cell lines SW480 and HCT116 were treated with metformin. The viability, migration and invasion abilities of the cells were evaluated with the Cell Counting Kit-8, wound-healing and trans-well assay. The alterations of the [SNAIL/miR-34]:[ZEB/miR-200] system and the EMT markers E-cadherin and vimentin were detected by western blot, qPCR and immunofluorescent staining.Metformin exhibited inhibitory effects on the proliferation, migration and invasion of the CRC SW480 cells. The up-regulation of E-cadherin and the down-regulation of vimentin for both SW480 and HCT116 cells revealed the anti-EMT abilities of metformin. For the [SNAIL/miR-34]:[ZEB/miR-200] system, metformin increased miR-200a, miR-200c and miR-429 levels and decreased miR-34a, SNAIL1 and ZEB1 levels in the TGF-β-induced EMT. From immunofluorescence, we observed increased E-cadherin and ZEB1 co-expression in metformin-treated cells.Metformin may perform bidirectional regulations of the [SNAIL/miR-34]:[ZEB/miR-200] system in the EMT process for colorectal cancer. Such regulation is expressed as the inhibition of EMT in general as well as an increased higher proportion of E/M hybrid cells in the total population.