Objective To study the diagnostic value of MRI and CT in the preoperative staging of rectal cancer. Methods 80 cases of patients with rectal cancer confirmed by operation and pathology during January 2013 to January 2015 were selected as the research objects. All the patients received CT or MRI examination before operation with 40 cases in each group. The postoperative pathological clinical staging was taken as the gold standard to compared the diagnostic accuracy of CT and MRI in preoperative clinical T staging of rectal cancer and lymph nodes. Results Compared with the results of postoperative pathological T staging, the accuracy rates of CT in the diagnosis of stage T1-2, stage T3, stage T4 and total diagnosis were 57.1%, 72.2%, 66.7% and 67.5%, respectively while those of MRI were 87.5%, 84.2%, 76.9% and 82.5%, respectively. The total accurate rates of CT and MRI in the diagnosis of lymph nodes were 62.5% and 80% respectively. There was no significant difference in the total accuracy rates of CT and MRI in the diagnosis of preoperative T staging and lymph nodes (P>0.05). Conclusion The accuracy rates of MRI in the diagnosis of preoperative T staging and lymph node metastasis are higher than those of CT, but there is no significant difference.