Objective: To investigate the expression and significance of microRNA-224 (miR-224) in colon cancer cells. Methods: The miR-224 expression in four colon cancer cell lines (Caco-2, HCT116, HT-29 and LoVo) and normal colonic mucosal tissue were detected by real-time RT-PCR; HCT116 cells were transfected with miR-224 mimics or scrambled negative control sequence respectively, using the untreated HCT116 cells as blank control, and then the miR-224 expression was determined by real-time PCR, proliferation status was measured by MTT assay and plate colony formation assay, and cell cycle phase distribution was analyzed by flow cytometry in each group of cells. Results: The miR-224 expression in each of the four colon cancer cell lines was higher than that in normal colonic mucosal tissue (all P<0.05). Compared with the HCT116 cells in blank control group, the miR-224 expression was significantly increased, proliferative ability was significantly enhanced, the number of colonies was significantly augmented (all P<0.05), and G1 to S phase transition showed an accelerating trend as well (P=0.074) in those in miR-224 mimics tranfection group; the differences in all the observed indexes showed no statistical significance in those in negative control sequence transfection group (all P>0.05). Conclusion: The miR-224 expression is up-regulated in colon cancer cells, which may promote cell proliferation and cell cycle progression, and thereby play a cancer-promoting gene role in the pathogenesis of colon cancer.