Abstract: Objective: To investigate the time period when the CT findings of Renal Cell Carcinoma (RCC) are optimally demonstrated. Methods: A total of 24 individuals proved by pathology had undergone dynamic spiral- CT (S- CT) scan. Dynamic scanning started at 14-17 seconds, with a scan interval of 4.9 seconds. Images were assessed in two ways: peer review and measurement of data. In addition, based on the slope of the contrast media uptake curve, T- DC types were ranked from the smallest to the biggest of slope as type A, B and C. Results: 1)The peer review for the CT images found that cortical phase (CP), nephrographic phase (NP) and excretory phase was at 22.4, 84.3, 114.9 seconds.The time when the CT features of RCC were optimally demonstrated was at 70.2 seconds. The earliest time for RCC CT features was measured at 23.9 seconds. 2)Image data analysis: (1) CP, NP and EP started at 17.3, 91.2 and 109.4seconds, respectively. (2) The time that the density (or CT value) of the tumor mass reached the peak enhancement was at 54 seconds for RCC. The time of the maximal difference of densities between tumor and renal parenchyma was at 102 seconds. Conclusions: The optimization of temporary window for detecting and characterizing RCC is recommended: a dynamic CT scan is to be programmed at scan delay time of 24, 38, 70, 100 seconds, followed by a complete renal S- CT scan.