Objective To determine the influence of combinative assessment of transrectal ultrasound (TRUS) and serum amyloid A protein (SAA) on the assessment of preoperative staging selection of operative procedures in the middle and lower rectal cancer. Methods Prospectively enrolled 130 patients, who diagnosed definitely as middle and lower rectal cancer at West China Hospital of Sichuan University from June 2008 to February 2009 were randomly assigned into two groups with 65 participants, respectively. In one group named TRUS combined SAA group, both TRUS and SAA combinative assessment were made for the preoperative evaluation. In another group named TRUS group, only the preoperative TRUS was made. The preoperative staging and predicted operative procedures were compared with postoperative pathologic staging and practical operation program, respectively.Results Of 118 patients with rectal cancer were actually included into TRUS combined SAA group (n=59) and TRUS group (n=59). The baselines of characteristics of two groups were basically identical. For TRUS combined SAA group， the accuracies of preoperative T and N staging were 79.7% (47/59) and 77.8% (42/54) respectively; For TRUS group the corresponding rates were 86.4% (51/59) and 57.7% (30/52), respectively. There was no statistically significant difference of the accuracy of preoperative T staging （P=0.609） while preoperative N staging had statistical difference (P=0.027) between two groups. There was a statistically significant difference of the accuracy of prediction to operative procedures in two groups 〔96.6% (57/59) vs. 83.1% (49/59), P=0.015〕. The preoperative T staging was related to the selection of operative procedures (P=0.037) when analyzing the relationship between the operative procedures and the multiple clinicopathological factors in middle and lower rectal cancer. ConclusionCombinative assessment of TRUS and SAA could improve the accuracy of preoperative staging in middle and lower rectal cancer, thus provide higher predictive coincidence rate to operative procedures for surgeon.