Objective: To evaluate the nephrotoxic effects of ionic contrast media (ICM)and nonionic contrast media (NCM). Methods: ICM and NCM was compared in 160 patients undergoing enchanced CT scan in a prospective, randomized, double blind multicenter trial, 90 with normal renal function(NRF) were divided into two groups: using ICM and NCM,70 with slight impaired renal function(IRF) were divided into two groups:using ICM AND using NCM. A sample of fresh urine and a venous blood sample were obtained from all patients 24 hours before and 24 hours, 48 hours, 72 hours after used contrast media to determine serum creatinine and β 2 microglobulin, urinary creatinine and β 2 microglobulin. Results: ①serum creatinine and β 2 microglobulin,urinary creatinine and β 2 microglobulin after 24h and 48h in patients with NRF using ICM were increased. There was a statistically significant difference between the values before 24h and 24h, 48h after using CM. But the values 72h after was come back basic values. There was not a statistically significant difference between the values before and after using NCM in patients with NRF.②serum creatinine and β 2 microglobulin after 24h and 48h in patients with NRF using ICM were increased ( P <0.01). The values 72h after was not come back basic values. There was not a statistically significant difference between the values before and after using NCM in patients with IRF ( P <0.01). Conclusion:These findings suggest that the large dose of ICM has brief lesion to kidney. Using NCM has more safety and toleration to patients with INF.