Background: Long-term therapy with doxorubicin is associated with a high incidenceof a cumulative and irreversible dilated cardiomyopathy, despite of its broad anti-neoplastic effectiveness. The goal of this study was to evaluate the cardioprotective effects and safety of seapolyphenol (polyphenol purifi ed from Ecklonia cava) against doxorubicin-induced cardiotoxicity in an animal rat model. Methods and Results: In total 21 rats including doxorubicin and control groups, baseline and 6 weeks follow up echocardiography were practiced. Left ventricular ejection fraction signifi cantly decreased and the left ventricular end diastolic/systolic dimension and LV mass index signifi cantly increased in single doxorubicin group compared to seapolynol plus doxorubicin group. Also, electron microscopic fi nding showed less impaired myofi ber and mitochondria in seapolynol plus doxorubicin group than in single doxorubicin group. Conclusions: Our data showed that seapolynol had cardioprotective effects against doxorubicin-induced cardiotoxicity in an animal rat model with the evidence of electron microscopic fi nding in addition to echocardiographic results.