Objective To investigate the long-term effects of contrast medium on renal function in a rat contrast-induced nephropathy (CIN) modle. Methods Forty-eight SD rats were pretreated intravenously with L-NG-nitroarginine methyl ester (L-NAME 10 mg/kg) and indomethacin (10 mg/kg). Then 30 minutes later diatrizoate (DTZ 8 mL/kg) was administrated in test group (n=24) to establish contrast-induced acute renal injury models, and saline (8 mL/kg) was injectd in control group (n=24). Renal function and histopathological changes were monitored at 24 hours, and at the end of 1^st, 2^nd and 3^rd month after the administration. Results There was no significant difference of serum creatinine baseline value between test and control group. Twenty-four hours after DTZ injection, serum creatinine in test group increased significantly from (48.02±5.53) μmol/L to (112.7±45.35) μmol/L (P<0.001). Meanwhile, the pathological changes were characterized by extensive cytoplasmic disruption, interstitial congestion and edema, especially in the outer medulla. Although serum creatinine dropped back to the baseline 3 months after DTZ injection in test group, focal interstitial inflamation still existed, and rave lesions of the tubulointerstitium were partly replaced by fibrous tissues. Conclusions Renal function of the SD rats may not recover completely 3 months after DTZ administration as the maintenance of chronic tubulointerstitial lesions.