Objective To study the effect of age on iodinated contrast induced acute kidney injury (CI-AKI) in male rats. Methods According to the age category, 36 healthy SD male rats were divided into three age groups (n=12/group), including 4 months, 12 months and 24 months group, and then each age group were randomly divided into control group and contrast media(CM) group(n = 6). After 24 h water deprivation, all three CM groups were intravascularly injected with 76% diatrizoate (10 ml/kg) through a caudal vein. The other three control groups were injected with equal volumes of saline in parallel. Urine creatinine (UCr), enzyme activity of urine N-acetyl-beta-D-glucosaminidase(UNAG), serum creatinine (SCr), creatinine clearance rate (Ccr), malondialdehyde (MDA) level and angiotensin-converting enzyme(ACE) activity were determined. The rats were sacrificed after 48 h. Then pathological changes of the right kidney tissue and the expression of Sp1 protein in the renal tissue were examined. Results At 48 h after CM administration, 24 months rats showed a significant increase in SCr by＞25% from baseline (P＜0.01) and a decline in Ccr (P＜0.05); the levels of ACE and MDA in renal tissues and scores of tubular injury were also increased (P＜0.01); the expression of Sp1 protein in renal tissue was significantly upregulated (P＜0.05). At 24 h after CM administration, the enzyme activity of UNAG was significantly higher(P＜0.001). In 12 months rats with CM injection, the level of SCr was increased by <25% from baseline(P＜0.05). There was an increasing trend but no significant statistic difference in levels of MDA and ACE in renal tissue, scores of tubular injury, and expression of Sp1 protein between control group and CM group of 12 months rats. There was no difference between control group and CM group of 4 months rats in all above parameters (P>0.05). Conclusion Aging is a risk factor for CI-AKI in rat. Oxidative stress, ACE, and transcription factor Sp1 play a role in nephrotoxcity induced by iodinated contrast media in the aging male rats.