Gallic acid has been reported to mitigate cardiac hypertrophy, fibrosis and arterial hypertension. The effects of syringic acid, a derivative of gallic acid, on cardiac hypertrophy and fibrosis have not been previously investigated. This study aimed to examine the effects of syringic acid on isoproterenol-treated mice and cells. Syringic acid mitigated the isoproterenol-induced upregulation of heart weight to bodyweight ratio, pathological cardiac remodelling and fibrosis in mice. Picrosirius red staining, quantitative real-time polymerase chain reaction (qRT-PCR) and Western blotting analyses revealed that syringic acid markedly downregulated collagen accumulation and fibrosis-related factors, including Fn1. The results of RNA sequencing analysis of Ereg expression were verified using qRT-PCR. Syringic acid or transfection with si-Ereg mitigated the isoproterenol-induced upregulation of Ereg, Myc and Ngfr. Ereg knockdown mitigated the isoproterenol-induced upregulation of Nppb and Fn1 and enhancement of cell size. Mechanistically, syringic acid alleviated cardiac hypertrophy and fibrosis by downregulating Ereg. These results suggest that syringic acid is a potential therapeutic agent for cardiac hypertrophy and fibrosis.