Radioresistance is a material obstacle for effective treatment of colorectal cancer (CRC). Thus, the discovery of a novel biomarker for determining the CRC radiosensitivity is necessary. Recent studies have confirmed that miR-183-3p regulates cell phenotypes and tumor growth in various cancers. However, the role and mechanism of this micro-ribonucleic acid in CRC radiosensitivity remains unclear. Here, the abundances of miR-183-5p and ATG5 mRNAwere detected by a real-time quantitative reverse transcription polymerase chain reaction. Kaplan-Meier survival analysis was carried out to explore the correlation between miR-183-5p and patient prognosis. Cell viability was evaluated by the MTT assay. Survival fraction analysis through colony formation was performed to assess the cell radiation response. Bioinformatic, luciferase and western blot assays were employed to verify the targeted interaction between miR-183-5p and ATG5. The results showed that an elevated abundance of miR-183-5p and a reduced ATG5 level in CRC were associated with the poor prognosis. The knockdown of miR-183-5p enhanced the sensitivity of CRC cells to radiation, inflected by the decreased cell viability and survival fraction. Mechanically, ATG5 was targeted by miR-183-5p. The addition of ATG5 conferred the radiosensitivity of the CRC cells, which was revered by miR-183-5p restoration. Furthermore, miR-183-5p knockdown hindered the tumor growth by repressing ATG5 in vivo after radiation treatment. In summary, the output data indicated that miR-183-5p heightened the radiation response of the CRC cells by targeting ATG5, promising a novel therapeutic target for CRC patients with radioresistance.