A B S T R A C TBackground: Alteration of kidney function called Contrast-Induced Nephropathy (CIN) is commonly encountered in diagnostic and interventional cardiology procedures. It results in considerable morbidity and mortality besides imposing significant costs on the healthcare system. Today, it is accounted as the third cause of hospital-acquired acute renal failure. Objectives: Considering anti-oxidant and free radical scavenging properties of selenium and the role of free radicals in CIN, the present study aimed to investigate the effects of oral selenium (in the form of Se-yeast capsule) on preventing or decreasing the rate of CIN in patients undergoing angiography and angioplasty. Patients and Methods: This prospective, non-randomized, single-blind, single-center clinical trial was conducted on 175 consecutive patients admitted for elective coronary angiography (N = 105) or angioplasty (N = 70). Selenium was prescribed as a single dose of 200 micrograms the day before and after the procedure. Routine hydration based on the ward protocol was administered for all the patients. For the control group, the researchers made use of the data of another survey performed in the same hospitals for determining the prevalence of CIN a year before. The data were analyzed using student's t-test and logistic regression analysis and P < 0.05 was considered as statistically significant. Results: Based on the results of student's t-test, the mean difference between the two groups was significant only in hematocrit levels. The incidence of CIN was 9% in the selenium group compared to 22% in the control group (P = 0.027). There was no case of in-hospital mortality and none of the CIN patients required renal replacement therapy during hospitalization. Conclusions: Prophylactic selenium administration may significantly reduce the incidence of CIN.