Abstract: Objective To explore the expression and clinical significance of microRNA203 （miR-203） in colorectal cancer， and to verify its function in colorectal carcinoma cells. Methods The realtime quantitative PCR （qRT-PCR） was used to detect the levels of miR-203 in 52 cases of colorectal cancer and corresponding adjacent tissues. The relationship between the levels of miR203 and clinical pathological parameters （gender， age， tumor size， tumor location， tumor differentiation， clinical stage and lymph node metastasis） and preoperative carcinoembryonic antigen was carried out. The levels of miR203 in three common colorectal cancer cell lines （SW480， Lovo and HT-29） and human normal colonic mucosal epithelial cells NCM460 were also measured via qRTPCR. The cell with the lowest miR-203 level was chosen and then subjected to the transfection with miR-203 analogue （mimics） and miR-203 control, respectively. The influences of miR-203 mimics on the cell proliferation， invasion and apoptosis were evaluated by MTT method， flow cytometry with PI／Annexin V double staining and Transwell， respectively. Results The relative expression of miR-203 in colorectal cancer tissues was 0.372±0.019， lower than that in paracarcinoma tissues. The levels of miR-203 were related with TNM staging， lymph node metastasis， tumor size and preoperative carcinoembryonic antigen levels. When the miR203 level in NCM460 cell was taken as reference （1.00）， the relative expression of miR-203 in SW480， Lovo and HT-29 cells were 0.26±0.07， 0.44± 0.05 and 0.32±0.04， respectively. As shown in the MTT analysis， the absorption values of miR-203 mimics group were lower than the miR203 control group at 48， 72 and 96 h （P＜0.05）. Moreover， there were higher apoptotic rates but lower transmembrane cell numbers in miR-203 mimics group versus miR203 control group at 48 and 96 h. Conclusion There are low levels of miR-203 in both colorectal cancer tissues and cells. The elevation of miR-203 can inhibit the cell proliferation and invasion but induce the apoptosis in colorectal cancer.