Rosmarinic acid (RA) is a naturally occurring polyphenolic and is found in several herbs in the Lamiaceae family, such as, Perilla frutescens. ADR is a potent anti-tumor drug, but is unfortunately potently cardiotoxic. This study was undertaken to investigate the inhibitory effect of RA on ADR-induced apoptosis in H9c2 cardiac muscle cells at a mechanistic level. In vitro, ADR significantly decreased the viabilities of H9c2 cells, and this was accompanied by apoptotic features, such as a change in nuclear morphology and caspase protease activation. RA was found to markedly inhibit these apoptotic characteristics by reducing intracellular ROS generation and by recovering the mitochondria membrane potential (delta psi). In addition, RA reversed the downregulations of GSH, SOD and Bcl-2 by ADR. In the present study, ADR was found to activate c-Jun N-terminal kinase (JNK) and extracellular signal-regulated kinase (ERK), transcriptional factor-activator-protein (AP)-1. We found that c-fos, Jun-B, Jun-D and p-c-Jun were super shifted by ADR, indicating that these proteins have an important role in the ADR-induced AP-1 activation. The inhibitions of JNK and ERK using appropriate inhibitors or dominant negative cell lines reduced ADR-induced apoptosis in H9c2 cardiac muscle cells. Taken together, these results suggest that RA can inhibit ADR-induced apoptosis in H9C2 cardiac muscle cells by inhibiting ROS generation and JNK and ERK activation. Thus, we propose that RA should be viewed as a potential chemotherapeutic that inhibits cardiotoxicity in ADR-exposed patients.