Ginsenoside Rg(1) (Rg(1)), one of the active components of Panax ginseng, has been reported to inhibit proliferation of vascular smooth muscle cells induced by tumor necrosis factor-alpha. This study aims to investigate whether Rg(1) has protective effect on rat left ventricular hypertrophy and to probe its protective mechanisms. The rat left ventricular hypertrophy was induced by abdominal aorta coarctation and Rg(1) (3.75, 7.5 and 15 mg/kg/day) was given the day after surgery for 21 consecutive days. The left ventricular hypertrophy induced by abdominal aorta coarctation was evidenced by histopathology, electromicroscopy, and by determining the elevated left ventricular weight and the expression of atrial natriuretic peptide. Rg(1) significantly ameliorated left ventricular hypertrophy induced by abdominal aorta coarctation in a dose-dependent manner. To examine the mechanism of protection, the expressions of calcineurin, CnA (the catalytic subunit of calcineurin), extracellular signal-regulated kinase-1, and mitogen-activated protein (MAP) kinase phosphatase-1 were determined at the transcript and protein levels. The abdominal aorta coarctation induced increases in calcineurin, CnA, and extracellular signal-regulated kinase-1 expressions were suppressed, but the expression of MAP kinase phosphatase-1 was increased by Rg(1). These results demonstrate that Rg(1) alleviates left ventricular hypertrophy induced by abdominal aorta coarctation, and the protection appears to be due, at least in part, to its inhibitory effects on calcineurin and MAP kinase signaling pathways.