Recent studies show that long intergenic noncoding RNA-p21 (lincRNA-p21) is aberrantly expressed in several types of cancer, including colorectal cancer (CRC), one of the most common cancers in the world. Radiotherapy is considered as a standard preoperative treatment approach to reduce local recurrence for local advanced rectal cancer. However, a considerable number of rectal cancers are resistant to radiotherapy. In the present study, we evaluated the role of lincRNA‑p21 in radiotherapy for CRC and detected the possible molecular mechanism. By expression profile analysis, we demonstrated that lincRNA-p21 decreases in CRC cell lines and tissue samples, which contributes to the elevation of β-catenin in CRC. We further showed that lincRNA‑p21 increases following X-ray treatment, and enforced expression of the lincRNA enhances the sensitivity of radiotherapy for CRC by promoting cell apoptosis. Suppression of the β-catenin signaling pathway and elevation of the pro-apoptosis gene Noxa expression may help explain the role of lincRNA-p21 in CRC radiotherapy. The present study not only deepens our understanding of the mechanism of radiotherapy for CRC, but it also provides a potential target for CRC radiotherapy.