【Abstract】 Objective To investigate the diagnostic value of the mesorectum involved by respectable rectal carcinoma on magnetic resonance imaging(MRI). Methods From May 2014 to October 2016, 52 patients with rectal cancer confirmed by surgical pathology were recruited in this study. All patients underwent routine MRI scans and a threedimensional volume of the ultrafast multiphase dynamic contrastenhanced scans (LAVA) acquisition before operation, and the appearances of the mesorectum involved by rectal carcinoma were reviewed on MRI. The imaging findings were compared with pathological findings, and the Kappa analysis was used to test the agreement between the pathologic and radiologic results. Results Thirty cases of rectal carcinoma involving mesorectum and 22 cases of rectal carcinoma without mesorectum involvement were confirmed by postoperative pathological findings, respectively. In this enrolled cohort, 46 cases, 2 cases and 4 cases were correctly diagnosed, misdiagnosed and missed diagnosed by MRI, respectively. Mesorectum directly involved by rectal carcinoma occurred in 11 cases, and mesorectum involved by rectal carcinoma and lymphnode metastasis occurred in 19 cases. The diagnostic accuracy, sensitivity, specificity, positive predictive value and negative predictive value of MRI in the invasion of mesorectum by rectal cancer were 8846% (46/52), 8667% (26/30), 9091% (20/22), 9286% (26/28) and 8333% (20/24), respectively. The agreement between the pathologic and radiologic findings were good (Kappa=0766, P＜0001). Conclusion MRI can accurately locate the tumor and depict the mesorectum involved by rectal carcinoma.