Human microRNA-155 (miR-155) has been demonstrated to regulate a variety of cellular functions, including epithelial-to-mesenchymal transition (EMT) by targeting multiple messenger RNAs (mRNAs). However, its role in colorectal cancer (CRC) remains unelucidated. Therefore, the aim of the present study was to investigate the effects of miR-155 on CRC cells. The expression level of miR-155 was quantified by quantitative real-time reverse transcriptase-PCR (qRT-PCR) in primary CRC tissues and normal adjacent mucosa. MTT, migration and invasion assays were used to examine the proliferation, migration and invasion of SW480 cells transfected with miR‑155. The expression of miR-155 was significantly upregulated in the CRC tissues and the high expression of miR-155 correlated with an advanced clinical stage, lymph node and distant metastases. The ectopic expression of miR-155 enhanced the migration and invasive ability of the SW480 cells and altered their morphological appearance; however, cell proliferation was not affected. E-cadherin expression levels decreased, while ZEB1 expression levels increased in the SW480 cells overexpressing miR-155. Furthermore, the overexpression of miR-155 upregulated claudin-1 expression. Thus, our data suggest that miR-155 plays an important role in promoting CRC cell migration and invasion, at least in part through the regulation of claudin-1 expression and controlling metastasis in CRC.