Objective To study the clinical value of magnetic resonance imaging (MRI) and computed tomography (CT) in evaluating the preoperative T stage of rectal cancer. Methods A total of 62 patients with rectal cancer treated in the hospital from March 2013 to March 2016were selected as subjects. All patients were treated by total mesorectal excision and were examined with MRI and CT before operation.The sensitivity, specificity, positive predictive value, negative predictive value and accuracy of MRI and CT findings in the diagnosis of T stage of rectal cancer were calculated with the histopathological results as the golden standard. Results Compared with postoperative pathology, MRI examination showed that the staging was correct in 52 cases, insufficient in 3 cases and too high in 7 cases. The diagnostic accordance rates of MRI for stage T1, T2, T3 and T4 of rectal cancer were 95.2%, 90.3%, 88.7% and 93.5%, respectively, and the total accordance rate was 83.9%, Kappa value was 0.746. CT examination showed that the staging was correct in 40 cases, insufficient in 8 cases and too high in 14 cases. The diagnostic accordance rates of MRI for stage T1, T2, T3 and T4 of rectal cancer were 91.9%, 80.6%, 72.6% and 83.9%, respectively, and the total accordance rate was 64.5%, Kappa value was 0.470. The accordance rate of MRI in the diagnosis of stage T3 and the total accordance rate in the diagnosis of T stage of rectal cancer were significantly higher than those of CT(P<0.05). Conclusion MRI is more accurate than CT in the diagnosis of T stage of rectal cancer, which is of important guiding significance for the treatment of rectal cancer.