Deletion of microsomal prostaglandin E2 synthase-1 (mPGES-1) inhibits inflammation and protects against atherosclerotic vascular diseases but displayed variable influence on pathologic cardiac remodeling. Overactivation of β-adrenergic receptors (β-ARs) causes heart dysfunction and cardiac remodeling, whereas the role of mPGES-1 in β-AR-induced cardiac remodeling is unknown. Here we addressed this question using mPGES-1 knockout mice, subjecting them to isoproterenol, a synthetic nonselective agonist for β-ARs, at 5 or 15 mg/kg per day to induce different degrees of cardiac remodeling in vivo. Cardiac structure and function were assessed by echocardiography 24 hours after the last of seven consecutive daily injections of isoproterenol, and cardiac fibrosis was examined by Masson trichrome stain in morphology and by real-time polymerase chain reaction for the expression of fibrosis-related genes. The results showed that deletion of mPGES-1 had no significant effect on isoproterenol-induced cardiac dysfunction or hypertrophy. However, the cardiac fibrosis was dramatically attenuated in the mPGES-1 knockout mice after either low-dose or high-dose isoproterenol exposure. Furthermore, in vitro study revealed that overexpression of mPGES-1 in cultured cardiac fibroblasts increased isoproterenol-induced fibrosis, whereas knocking down mPGES-1 in cardiac myocytes decreased the fibrogenesis of fibroblasts. In conclusion, mPGES-1 deletion protects against isoproterenol-induced cardiac fibrosis in mice, and targeting mPGES-1 may represent a novel strategy to attenuate pathologic cardiac fibrosis, induced by β-AR agonists. SIGNIFICANCE STATEMENT: Inhibitors of microsomal prostaglandin E2 synthase-1 (mPGES-1) are being developed as alternative analgesics that are less likely to elicit cardiovascular hazards than cyclooxygenase-2 selective nonsteroidal anti-inflammatory drugs. We have demonstrated that deletion of mPGES-1 protects inflammatory vascular diseases and promotes post-myocardial infarction survival. The role of mPGES-1 in β-adrenergic receptor-induced cardiomyopathy is unknown. Here we illustrated that deletion of mPGES-1 alleviated isoproterenol-induced cardiac fibrosis without deteriorating cardiac dysfunction. These results illustrated that targeting mPGES-1 may represent an efficacious approach to the treatment of inflammatory cardiovascular diseases.