Portal vein thrombosis (PVT) is a vasculature hepatic disorder that involves a clot of blood in the hepatic portal vein, leading to elevated portal pressure and reduced supply of blood to the liver. PVT may be benign or malignant in patients with hepatocellular carcinoma and liver cirrhosis. The prognosis and course of treatment for these patients depend on the diagnosis and characterization of PVT. CT with contrast has high sensitivity and specificity in differentiation between benign and malignant PV thrombi. Portal venous phase contrast enhanced examination is the only one that can consistently make the diagnosis. The research enrolled 25 cases with liver cirrhosis and PVT, those patients underwent CT with contrast in Radiology department, Kafr El-Sheikh Liver and Heart Institute Research Center. History taking, pelviabdominal ultrasound using (GE vivid S5) with curvilinear probe (4 MHZ), color doppler and Triphasic C.T using Toshiba Aquilion one 16-slice 64  detector C.T scanner were performed to all patients. Concerning the final diagnosis of the PV thrombus, it demonstrated that 18 patients (72%) had benign thrombus and 7 patients (28%) had malignant thrombus. It was found that patients with malignant thrombi were all having thrombi extending from HCC (100%) in contrast to the patients with benign thrombi who were all having direct thrombi (100%), with significant variation (p<0.001). There was a considerable difference between the two groups in the arterial enhancement of the thrombus (85.7% in malignant thrombi vs. 0% in benign thrombi, p <0.001), and the mean HU density is higher in malignant thrombi (95.71 ± 11.04 in malignant thrombi vs. 41.67 ± 10.34 in benign thrombi, p<0.001). Triphasic C.T in differentiation between benign and malignant portal vein thrombi depends on thrombus enhancement in arterial phase of triphasic CT and thrombus density measured by HU.