Abstract: Objective To investigate the protective effect of genistein (Gen) on doxorubicin (Dox) induced cardiotoxicity and its possible mechanism. Methods A total of 24 SD rats were randomly divided into four groups: a control (Ctrl) group, a genistein (Gen) group, a doxorubicin (Dox) induced group and a genistein treatment (Gen+Dox) group. Except the Ctrl group, the other groups were given corresponding drugs for six weeks. After administration, rat heart weight/body weight ratio and body length/tail length ratio were calculated. Fasting blood samples were collected to detect the contents of creatine kinase(CK) and lactate dehydrogenase (LDH). HE staining was used to observe the morphological changes of myocardial tissue in rats. Immunohistochemistry was used to examine the expression of Caspase-3 in myocardial tissues. A dyeing semi-quantitative method with superoxide anion fluorescent probe (dihydroethidium, DHE) was used to detect the fluorescent expression of rat myocardial H9C2 cells. The expression of apoptotic protein Caspase-3 was detected by Western blot. Results The heart weight/body weight ratio and body length/tail length ratio slightly changed in each group, without statistical differences group(P>0.05). Compared with the Ctrl group, the contents of serum CK and LDH remarkably increased in the Dox group(P<0.01), but decreased in the Gen + Dox group (P<0.01). The myocardial tissue in the Dox group showed patchlike necrosis, increased myocardial fibers and obvious apoptosis of myocardial cells, while the myocardial cells in the Gen+Dox group were neatly arranged, with clear structure and few myocardial fibers. Compared with the Ctrl group, the fluorescence expression of DHE and the expression of Caspase-3 protein in the Dox group were significantly up-regulated (P<0.05), but down-regulated after treatment with Gen (P0.01). Conclusions Gen may reduce the cardiotoxicity induced by doxorubicin by alleviating oxidative stress and down-regulating the expression of Caspase-3 protein, so as to play a protective role in the cardiotoxicity induced by doxorubicin.