Objective To compare diagnosis values of computed tomography (CT) and magnetic resonance imaging (MRI) in preoperative staging of rectal carcinoma. Methods The imaging data of 81 patients with rectal carcinoma from January 2013 to January 2017 in the Hefei Second People’s Hospital were retrospectively analyzed. Based on the postoperative pathological results, the diagnostic accordance rates of CT and MRI on the T staging and N staging were calculated. Results The sensitivities of the CT and MRI on the preoperative T staging of rectal carcinoma were 69.1% (56/81) and 82.5% (52/63), the difference was not statistically significant (χ2=3.396, P=0.065), the Kappa values was 0.521 and 0.371, respectively, the MRI on the T staging was in a good agreement with the pathological diagnosis. The sensitivitie of the T1-2, T3, and T4 stagings with CT was 70.0%, 66.7%, and 72.0%, respectively, with MRI was 83.3%, 83.3%, and 81.0%, respectively, which had no significant difference respectively between the CT and the MRI. The areas under the receiver operating characteristic curve of the T1-2, T3, and T4 stagings with the CT and MRI were 0.809, 0.689, 0.798 and 0.897, 0.826, 0.869, respectively. The sensitivities of the CT and MRI on the preoperative N staging of rectal carcinoma were 59.3% (48/81) and 65.1% (41/63), the difference was not statistically significant (χ2=0.509, P=0.476), the Kappa values were 0.371 and 0.463, respectively. The sensitivities of the N0, N1, N2 stagings with CT were 64.7%, 45.5%, 64.0%, with MRI were 70.3%, 63.2%, 72.5%, which had no significant difference respectively between the CT and the MRI. Conclusions Results of in this study show that MRI is superior to CT for judgment of tumor infiltration. Neither CT nor MRI is able to provide satisfactory assessment of lymph node metastasis.