α(1)-Adrenergic receptor (α(1)-AR) is a crucial mediator of cardiac hypertrophy. Although numerous intracellular pathways have been implicated in α(1)-AR-induced hypertrophy, its precise mechanism remains elusive. We aimed to determine whether α(1)-AR induces cardiac hypertrophy through a novel signaling pathway-α(1)-AR/epidermal growth factor receptor (EGFR)/signal transducer and activator of transcription 3 (STAT3). The activation of STAT3 by α(1)-AR was first demonstrated by tyrosine phosphorylation, nuclear translocation, DNA binding, and transcriptional activity in neonatal Sprague-Dawley rat cardiomyocytes. Activated STAT3 showed an essential role in α(1)-AR-induced cardiomyocyte hypertrophic growth, as assessed by treatment with STAT3 inhibitory peptide and lentivirus-STAT3 small interfering RNA. The results were further confirmed by in vivo experiments involving intraperitoneal injection of the STAT3 inhibitor WP1066 significantly inhibiting phenylephrine-infusion-induced heart hypertrophy in male C57BL/6 mice. Furthermore, the α(1)-AR-activated STAT3 was associated with transactivation of EGFR because inhibition of EGFR with the selective inhibitor AG1478 prevented α(1)-AR-induced STAT3 tyrosine phosphorylation and its transcriptional activity, as well as cardiac hypertrophy. In summary, these results suggest that α(1)-AR induces the activation of STAT3, mainly through transactivation of EGFR, which plays an important role in α(1)-AR-induced cardiac hypertrophy.