Abstract: Objective To investigate the effects of X-ray dose on the expression of microRNA-221(miR-221) and p57kip2 in human colorectal carcinoma (CRC) cells. Methods Conventionally cultured Caco2 cells were divided into 5 groups with different doses of X-ray (0, 2, 4,6 and 8 Gy) respectively. The total RNA and protein of the cells were extracted after irradiation for 24 h,The expression level of miR-221 and p57^kip2 mRNA were detected by real-time Q-PCR. The expression of p57kip2 in cells was detected by Western blot analysis. Results The radiation dose of X-ray had signifi cant effect on the expression of miR-221 and p57kip2 protein in human Caco2 cells in a dose-dependent manner. The miR-221 expression level improved gradually with the increase of irradiation dose while the p57^kip2 protein expression level reduced gradually (P<0.05). Conclusion Radiation dose could affect the miR-221/p57^kip2 regulation pathways in CRC cells. Suppressed miR-221 expression may enhance the radiosensitivity of CRC cells.