Colorectal cancer (CRC) is still one of the most important neoplasias causing human death. Multidisciplinary therapy has won consensus in the management of CRC, of which, radiotherapy occupies an important position. However, radioresistance is still a major obstacle in local control of CRC. Overexpression of long non-coding RNA HOTAIR has been found to correlate with tumorigenesis and poor prognosis in several types of cancer. In the present study, we analyzed HOTAIR expression levels of 53 CRC patients in tumor and adjacent normal tissue by real-time quantitative PCR. Knockdown of HOTAIR by RNA interference was performed to explore its roles in cell proliferation, migration, invasion, apoptosis and radiosensitivity. Results showed that CRC patients had higher HOTAIR expression in tumor tissues compared with adjacent normal tissues. In vitro, down-regulation of HOTAIR reduced proliferation, migration and invasiveness while enhanced apoptosis and radiosensitivity of CRC cells. Taken together, our findings suggest that long non-coding RNA HOTAIR expression is closely associated with tumor invasion and radiosensitivity, indicating the potential role in diagnostics and therapeutics of CRC.