Aging causing changes in kidney functions and structure. This research aimed to determine protective effects of soy isoflavone oral administration for 8 weeks on kidneys of aged male albino rats and possible mechanisms of action. Thirty rats were used, 10 rats aged 3-5 months and 20 aged 20-24 months which develop age-dependent nephropathy. Rats divided into 3 equal groups; adult control and aged control groups fed on regular diet and aged treated group orally ingested 100 mg/kg soy isoflavone daily for 8 weeks. Serum levels of kidney functions (creatinine, uric acid, urea, and cystatin C) and oxidative stress biomarkers such as malonaldehyde (MDA), glutathione (GSH) and superoxide dismutase (SOD) assessed. Kidney structures examined by light microscopy. Aging produced functional and structural renal changes and impairment of oxidative stress versus Adult control. Soy isoflavone had renoprotective assessed by decreased serum levels of creatinine, uric acid, urea and cystatin C. These effects caused to isoflavone antioxidant properties as evident by decline in serum levels of MDA, while GSH and SOD increased. Kidney structure as renal cortical thickness and tubular structure improved after treatment. Data demonstrated renoprotective action of isoflavone in aged kidney, by reducing oxidative stress and increasing antioxidants.