Abstract: Objective：To evaluate the diagnostic value of ultrasound and MRI in preoperative staging of rectal cancer. Methods：A retrospective analysis of preoperative MRI and ultrasound in patients with pathologically proved rectal cancer was performed. The diagnostic values of ultrasound and MRI in preoperative staging of rectal cancer were compared by using pathological diagnosis as the gold standard. Results：The accuracy of transrectal ultrasound was higher than that of MRI in the diagnosis of T1 rectal cancer, its accuracy was lower than that of MRI in the diagnosis of T4 rectal cancer, and the differences were statistically significant (P<0.05). The accuracy of MRI was higher than that of ultrasound in the diagnosis of N0 and N2 rectal cancer, and the differences were statistically significant (P<0.05). And the difference between MRI and ultrasound in the diagnosis of N1 rectal cancer was not statistically significant. The area under the curve (AUC) of ultrasound was less than that of MRI in the preoperative diagnosis of rectal cancer, but the difference was not statistically significant. Conclusions：Rectal cancer of different pathological grades should be examined by different methods. MRI should be chosen for suspected advanced rectal cancer patients in preoperative staging diagnosis, and ultrasound should be selected for lowergrade rectal cancer or followup process.