Ginsenoside Rg1 (Rg1), one of the active ingredients in Panax ginseng, has been known to regulate many cellular processes. The purpose of this study was to investigate the protective effects of Rg1 on apoptosis in mouse cultured astrocytes in vitro and a mouse model of cerebral ischemia and reperfusion in vivo. The cell apoptosis was measured by fluorescence microplate reader and xCELLigence system and the Ca(2+) overload was recorded by confocal microscopy. The mitochondrial membrane potential and reactive oxygen species (ROS) were determined by flow cytometry. BALB/c mice were subjected to transient middle cerebral artery occlusion (MCAO) and randomly divided into four groups: Sham (sham-operated +0.9% saline), MCAO (MCAO+0.9% saline), Rg1-L (MCAO+Rg1 20 mg/kg) and Rg1-H (MCAO+Rg1 40 mg/kg). Neurological deficit scores, brain water content and infarct volume were evaluated at 24 h after reperfusion. The results showed that Rg1 significantly attenuated H2O2-induced apoptosis in astrocytes. Rg1 efficiently inhibited intracellular Ca(2+) overload, loss of mitochondrial membrane potential, and ROS production in astrocytes. In vivo study, it was also observed that Rg1 markedly reduced the neurological deficit scores, brain edema, and infarct volume in the model mice. These results suggest that Rg1 possesses significant neuroprotective effects, which might be related to the prevention of astrocytes from apoptosis.