The ingestion of excessive amounts of the fluoride ion (F) may cause chronic fluorosis with abnormalities in many organs and systems including, in addition to dental and skeletal fluorosis, impaired renal function. The aim of the present study was to investigate renal function and the levels of advanced oxidation protein products (AOPP) as oxidative stress markers in chronically fluorotic sheep with kidney disease. Fifteen healthy and 30 fluorotic sheep were studied. The plasma F levels were determined with a F-selective electrode. The plasma AOPP and the serum total protein levels were measured spectrophotometrically. The serum BUN, creatinine, potassium, sodium, and chloride levels were determined by autoanalyzer. Compared to the control group, significant increases were present in the fluorotic sheep in the levels of F (p=0.001), AOPP (p=0.001), BUN (p=0.001), creatinine (p= 0.05), and total protein (p= 0.05). A significant decrease was present in the fluorotic sheep in the level of potassium (p=0.01) while no significant changes were present in the sodium and chloride concentrations. The levels of AOPP in chronically fluorotic sheep, reported here for the first time in veterinary science, and the biochemical abnormalities can be considered in the evaluation of the effects of chronic fluorosis on kidney function.