[ Objective]The aim of this study was to assess the value of ultrasonic probe (USP) under colonoscope in the preoperative staging of colorectal carcinoma. [ Methods]75 patients with colorectal carcinomas proven pathologically were given USP (Olympus UM-2R, 12MHz; UM -3R, 20 MHz) under colonoscope before operation. The results were compared with histopathologic findings of resected specimens. [ Results] Colorectal carcinoma appeared as a hypoechoic mass under USP. USP had an overall accuracy rate of 82.7% in the diagnosis of T staging of colorectal carcinoma. In determining lymph node metastasis , the sensitivity and specificity were 53.2% and 61.5%, the positive predictive value and the negative predictive value were 0.87 and 0. 22, respectively. [ Conclusions ] USP is valuable for the staging of colorectal carcinoma and has a high accuracy rate in determining the depth of tumor invasion. The preoperative information obtained by this tool may influence the choice of therapy.