Objective To determine the role of multi-slice spiral computed tomography (MSCT) compared with transrectal ultrasound (TRUS) in preoperative staging of rectal cancer. Methods Patients with rectal cancer from January to May 2009 in Department of Anal-Colorectal Surgery of West China Hospital were enrolled. All patients were preoperatively examined by both MSCT and TRUS for T and N staging, which were compared with postoperative pathological findings. Results The study population consisted of 81 patients. Regarding depth of tumor invasion, the accuracy of TRUS (88.89%) was not significantly higher than that of MSCT (77.78%), P=0.168. Regarding lymph node metastasis, the result of MSCT was more accurate than that of TRUS (66.67% vs. 48.15%, P=0.034). Conclusions Although TRUS remains the advantages in evaluating local invasion, the gap between MSCT and TRUS are significantly diminished. MSCT is superior to TRUS in evaluation of lymph node metastasis, however, further improvement on the diagnostic accuracies would be warranted in both modalities.