Increasing evidence has solidified the involvement of alpha-synuclein (alpha-Syn) and neurotoxins in the pathogenesis of Parkinson's disease (PD), suggesting a combination of genetic and environmental influences. 2,3,5,4'-Tetrahydroxystilbene-2-O--D-glucoside (TSG) is one of the main active components extracted from Polygonum multiflorum. The purpose of the present study was to investigate the effects of TSG on alpha-Syn aggregation, mitochondrial dysfunction, oxidative stress, and apoptosis in vitro. A53T mutant alpha-synuclein-transfected cells (A53T AS cells) plus MPP+ exposure were used as a complex cell model of PD. The expression of proteins was determined by Western blot assay. Flow cytometry was utilized to measure mitochondrial membrane potential and apoptosis. The results showed that MPP+ exposure for 24 h induced more severe damage in A53T AS cells than in vector control cells. Pretreatment of TSG for 24 h significantly increased the cell viability; decreased lactate dehydrogenase leakage; inhibited alpha-Syn over-expression and aggregation; elevated mitochondrial membrane potential; decreased reactive oxygen species, Bax/Bcl-2 ratio, and caspase-3 activity; and inhibited apoptosis in A53T AS cells exposed to MPP+. These results suggest that TSG may be an attractive candidate for PD therapy.