Doxorubicin belongs to anthracycline cytotoxic drugs and it is widely used as a major therapeutic agent in the treatment of various types of tumors. However,its therapeutic use is limited by the development of myelosuppression and cardiotoxicity after a specific cumulative dose is reached. The aim of this study was to investigate the effect of flavonoids, either natural or synthetic on doxorubicin-mediated formation of oxidative stress implicated in doxorubicin toxicity. Doxorubicin caused a concentration-dependent increase in the formation of hydroxyl radicals in minipig liver microsomes used as an in-vitro model system. When bacterial membranes heterologously expressing human NADPH cytochrome-P450 oxidoreductase were incubated with doxorubicin, formation of the superoxide radical under aerobic conditions and the doxorubicin–semiquinone radical under anaerobic conditions was detected. Forty different flavonoids were tested for their potency to prevent NADPH-induced or Fe2+-induced peroxidation of lipids in the microsomal system. According to the results, seven flavonoids were selected for evaluation of their potency to inhibit doxorubicin-dependent formation of hydroxyl radicals assessed by electron spin resonance. Myricetin, fisetin, and kaempferol were found to produce a significant protective effect against hydroxyl radicals in the minipig liver microsomal system. In conclusion, this study shows the use of a novel cost-effective in-vitro model system for preselection of antioxidants for testing of their protective effects against toxicity of anthracyclines and potentially other oxidative stress-inducing chemicals.