Abstract: ObjectiveTo study the toxicity of 1-methyl-4-phenylpyridinium ion (MPP⁺)on rat pheochrom ocytom a PC12 cells in vitra.MethodsPC12 cell cultures were exposed to 100, 300, 500 μmol/L MPP⁺.The inhibition of the cell proliferation was deteanined by MTT assay Western blot was performed to determine the level of phosphorylated extracellular signal-regulated protein kinase(ERK).ResultsMPP⁺ exposure inhibited the proliferation of PC12 cells in a dose-and time-dependentm anner.The inhibitory rates were 17.86%-58.06%.Western-blot showed that MPP⁺ decreased the phosphorylation of ERK1/2(P<0.01).PD98059, a selective inhibitor of MEK, further inhibited the proliferation of PC12 cells.ConclusionMPP⁺ can significantly inhibit the proliferation of PC12 cells The reduction of ERK1/2 phosphorylation could be an inportant molecular mechanism of MPP⁺-induced dopam inergic neurotoxicity.