【Objective】To measure the diameter of the superior rectal vein（SRV）& theinferior mesenteric vein（IMV）by CT and analyze their relationship with lymphatic metastasis of rectal carcinoma.And to discuss the feasibility of utilizing SRV to predict lymph node metastasis of rectal cancer.【Methods】The CT imaging and pathological data of 105 rectal carcinoma patients were ana? lyzed retrospectively. We measured and compared the diameter of every patient′s SRV & IMV by CT in the presence and absence of microvascular tumor thrombus，signet ring cell，lymph node metastasis and distant metastasis. The accuracy of predicting lymph node metastasis for rectal carcinoma by the diameter of SRV were evaluated by ROC curve.【Results】There were statistical differences in the diameters of SRV and IMV between rectal cancer group with lymph node metastasis（D = 4.34 mm，D = 5.00 mm）and without （D = 3.56 mm，D = 4.81 mm；P < 0.001，P = 0.023）. The differences were significant in the diameter of SRV between rectal cancer group with microvascular tumor thrombus or signet ring cell and without（P = 0.019，P = 0.044）. However，the diameter of IMV showed no statistical difference between rectal cancer group with microvascular tumor thrombus or signet ring cell and without（P = 0.605，P = 0.663）. And there was no statistical difference in the diameter of SRV or IMV between rectal cancer patients with distant metastasis and without（P > 0.05）. Regarding 3.75 mm as the cut-off value for the diameter of SRV to predict lymph node me? tastasis for rectal cancer patients，the sensitivity was 90.9% and the specificity was 82.0%. Regarding 4.65 mm as the cut-off value for the diameter of IMV to predict lymph node metastasis for rectal cancer patients，the sensitivity was 87.3% and the specificity was 38%.【Conclusions】It is completely feasible to utilize the diameter of SRV measured by CT to predict lymph node metastasis of rectal carcinoma with high sensitivity，accuracy，and relatively high specificity.