Abstract: Objective To detect the expression and the function of microRNA-31(miR-31) in colorectal cancer(CRC) tissues, and to predict its target genes and conduct bioinformatic analysis, so as to investigate its role and the regulation mechanism. Methods miR-31 expression were examined in 8 CRC cell lines, 40 CRC tissues and their matched normal tissues, and 33 adenoma tissues by quantitative reverse transcription PCR(qRT-PCR). The relationship between miR-31 expression and clinicopathological information were analyzed. MTS method was used to detect the cell growth of HCT116 in different groups, including miRControl, miR-31 mimics, miR-31 inhibitor and the blank groups. Western blot was used to detect the expression of proliferation cell nuclear antigen(PCNA) in miR-31 mimic and miR-31 inhibitor groups. Target genes of miR-31 were predicted by the software including TargetScan, DIANA-microT, miRanda, et al, and further to analyze the information by KEGG, GO(gene ontology) and signaling pathway enrichment. Results The relative expression levels of miR-31 in 8 CRC cell lines and tumor tissues were much higher than those in adenoma and normal tissues(P<0.05), however, there was no significant difference between adenoma and the normal tissues(t=0.122, P=0.904). No correlation was found between miR-31 expression and the clinicopathological variables of CRC(all P＞0.05). After transfection with miR-31 mimics, the expression level of miR-31 was remarkably up-regulated while down-regulated in miR-31 inhibitor group, compared with transfection with the miR-Control. Consequently, the cell grew faster in miR-31 mimics group, while the cell growth was inhibited in miR-31 inhibitor group, compared with the blank group and the miR-Control group(P<0.05). PCNA protein level in miR-31 inhibitor group was much lower than those in miR-31 mimics group and the blank group. The gene ontology analysis showed the function of predicted target genes of miR-31 concentrated on the regulation of post transcription and translation regulation, cell junction, migration and motility, etc.. And the KEGG pathway analysis showed the target genes mainly involved in endocytosis, axon guidence, T cell receptor signaling pathway, Wnt and MAPK signaling pathway. Conclusion The expression level of miR-31 is up-regulated in CRC tissues, and miR-31 could promote cell growth and proliferation. The predicted target genes of miR-31 provide some clues for CRC via regulating multiple biological processes.