Objective To explore the value of relative percentage washout (RPW) on enhanced CT in the differential diagnosis of renal cell carcinoma (pRCC) and hypervascular pancreatic neuroendocrine tumor (pNET) by comparing their imaging manifestations. Methods A retrospective analysis was made of the enhanced CT findings and RPW of 16 patients with 36 pRCCs confirmed by post-operative pathology and 25 patients with 28 hypervascular pNETs at the First Affiliated Hospital of Nanjing Medical University from January 2008 to December 2019. The two groups were compared in enhanced CT imaging features and RPW. SPSS statistics 25.0 was used for statistical analysis. Results There were statistically significant differences between the two groups in the tumor number, extrapancreatic metastasis and arterial enhanced CT value (P<0.05), but no statistically significant differences in the largest diameter, location, boundary, shape, intra-lesion necrosis, dilatation of the pancreatic duct and enhanced CT in the venous phase ( P>0.05 for all). RPW of the pRCC group (0.313±0.070) was significantly higher than that of the pNET group (0.195±0.096) (P<0.05). When the cut-off value was 0.21, receiver operating characteristic curve of RPW had good detection performance with area under the curve of 0.81, and sensitivity of 97.2% and specificity of 53.6%Conclusion pRCC and hypervascular pNET have distinctive imaging features and different RPW, which are helpful for their differential diagnosis.