GATA4 has been characterized as a crucial regulator of cardiac development and hypertrophy. Multiple signaling pathways involving MAPK contribute to GATA4 activation via direct phosphorylation. MSK and RSK are two kinase families mediating signal transduction downstream of the MAPK cascade. In this study, we investigated the effects of MSK and RSK on GATA4 activation. Overexpression of RSK2 greatly increased phosphorylation of GATA4 at Ser261. This phosphorylation enhanced its transcriptional and DNA binding activity. RSK-dependent phosphorylation of GATA4 also led to enhanced interaction with NKX2.5 and p300. Sequential phosphorylation of the ERK–RSK–GATA4 cascade and nuclear accumulation of RSK in cardiomyocytes were observed after phenylephrine treatment. Inhibition of RSK using the small molecule SL0101 abrogated GATA4 phosphorylation at Ser261, ultimately leading to a repression of fetal cardiac genes. Adenovirus-mediated overexpression of MSK1 had no direct effect on GATA4 phosphorylation but increased GATA4 expression. Together with GATA4 phosphorylation at Ser105 by ERK1/2, our findings show dual phosphorylation of GATA4 by the ERK–RSK cascade and suggest that MSK and RSK have distinct effects in PE-induced cardiac hypertrophic response.