Aim: To analyze the influence of the exogenous wild type alpha-synuclein α-synuclein) on the proliferation of MES23.5 dopaminergic neuronal cells and the molecular mechanism. Methods: The experiment was carried out in the Beijing Institute of Geriatrics between April and November 2005. Recombinant wild type human α-synuclein was added to the medium of MES23.5 dopaminergic neuronal cells. Immunofluorescent labeling and Western blot were used to detect the distribution of α-synuclein in the cells after 48-hour incubation. The growth curve was drawn with the MTS method to observe the proliferative rate cells. Gene chips technique was introduced to analyze the gene expression of the α- synuclein-treated cells. Results: Recombinant α-synuclein could enter into MES23.5 cells after addition to the culture medium and promote the proliferation of the cells. Of the α-synuclein-treated cells, 22 genes were found to be changed obviously, including 3 genes were correlated with endocytosis, 5 with transcription, 3 with protein synthesis, 3 with cell growth and proliferation, 4 with differentiation, 1 with proliferation and differentiation, 2 with generation of vesicle and neurotransmitter release, and 1 with cell cycle. Conclusion: Exogenous wild type α-synuclein can enter into MES23.5 dopaminergic neuronal cells by endocytosis, and then promote its proliferation, which may be correlated with its influence on the gene expression.