Summary.  The neuroprotective mechanism of Rg1 was studied in this paper by means of its obvious anti-apoptotic effect on human SHSY5Y cells. SHSY5Y cells were treated with MPP⁺ (1-methyl-4-phenyl-pyridinium) for 72 hours to induce apoptosis. During the apoptosis, production of reactive oxygen species (ROS), activation of c-Jun N-terminal kinase (JNK) and activation of caspase-3 were observed. The results showed that the signal transduction pathway of MPP⁺-induced apoptosis might be ROS to JNK, then to caspase-3. MPP⁺-induced apoptosis in SHSY5Y cells was obviously inhibited in both NAC (N-acetylcysteine) pretreated groups and Rg1 pretreated groups. Meanwhile, compared to that of the controls, our results showed decreased level of ROS, less JNK activity and lower expression of cleaved caspase-3 in pretreated NAC groups and in Rg1 pretreated groups. The protection by Rg1 might be mediated by removing of ROS. The removal of ROS might inhibit the activity of JNK and the expression of cleaved caspase-3. These results suggest that ginsenoside Rg1 may take effect through its anti-apoptotic activity in neurodegenerative diseases.