Hippophae rhamnoides L., also known as sea buckthorn (SBT), possesses a wide range of biological and pharmacological activities. However, the underlying mechanism is largely unknown. The present study examined whether SBT leaf extract could inhibit proliferation and promote apoptosis of rat glioma C6 cells. The results revealed that the treatment with SBT leaf extract inhibited proliferation of rat C6 glioma cells in a dose-dependent manner. SBT-induced reduction of C6 glioma cell proliferation and viability was accompanied by a decrease in production of reactive oxygen species (ROS), which are critical for the proliferation of tumor cells. SBT treatment not only significantly upregulated the expression of the pro-apoptotic protein Bcl-2-associated X (Bax) but also promoted its localization in the nucleus. Although increased expression and nuclear translocation of Bax were observed in SBT-treated C6 glioma cells, the induced nuclear morphological change was distinct from that of typical apoptotic cells in that most of SBT-treated cells were characterized by convoluted nuclei with cavitations and clumps of chromatin. All of these results suggest that SBT leaf extract could inhibit the rapid proliferation of rat C6 glioma cells, possibly by inducing the early events of apoptosis. Thus, SBT may serve as a potential therapeutic candidate for the treatment of glioma.