The study aimed to examine the antioxidizing effect of homoisoflavonoid in prophylactic administration under the conditions of renal ischemia-reperfusion in the laboratory rat. The pathological model for the in vivo experiment was unilateral renal ischemia-reperfusion of the laboratory rat. The animals were randomized into 5 groups. Homoisoflavonoid was administered to treated groups orally in doses of 5, 10 and 20 mg/kg once a day in 0.5% Avicel solution. The placebo group received Avicel only, and the intact group was without medication and intervention. On day 15 of the experiment, renal tissue ischemia/reperfusion (60/10 mins) was induced in the treated and placebo groups. Then the animals were exsanguinated, biochemical parameters in the blood (superoxidismutase, glutathionperoxidase, total antioxidizing capacity and malondialdehyde) were assayed, and renal samples were withdrawn for histopathological examination. A biochemical examination demonstrated a dependence of the effect of homoisoflavonoid on the dose administered. An obvious effect was demonstrated in the values of GSHPx, AOC, and MDA. On the other hand, a negative dependence was found between the dose of administered homoisoflavonoid and SOD and GSHPx values. The results of biochemical examination correlate with the histopathological pictures of the renal tissue and support the assumption about a protective effect of homoisoflavonoid under the conditions of artificially induced pathological state--renal tissue ischemia-reperfusion.