1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) causes nigrostriatal dopaminergic neurotoxicity and behavioral impairment in rodents, and previous studies suggest that nitric oxide and reactive oxygen species are involved in MPTP-induced neurotoxicity. The present study examines the effect of edaravone (3-methyl-1-phenyl-2-pyrazolin-5-one), a radical scavenger, on MPTP-induced neurotoxicity in the striatum and substantia nigra pars compacta (SNc) of C57BL/6J mice. MPTP treatment (10 mg/kg s.c. x 4 with 2-h intervals) decreased dopamine levels and tyrosine hydroxylase immunostaining in the striatum and SNc. Pretreatment with edaravone (1 and 3 mg/kg i.p.) significantly reduced the neurotoxicity in the SNc but not striatum. An immunohistochemical study showed that MPTP caused microglial activation both in the striatum and SNc, whereas it increased 3-nitrotyrosine immunoreactivity, an in vivo biomarker of peroxynitrite production, in the SNc but not the striatum. Furthermore, MPTP increased lipid peroxidation product thiobarbituric acid reactive substance in the midbrain, but not the striatum. Edaravone inhibited activation of the microglia and the increased 3-nitrotyrosine immunoreactivity in the SNc but not the striatum, and it also inhibited thiobarbituric acid reactive substance levels in the midbrain. Behavioral analyses showed that edaravone improved MPTP-induced impairment of locomotion and Rotorod performance. These results suggest that edaravone protects against MPTP-induced neurotoxicity in the SNc by blocking the production of reactive oxygen species or peroxynitrite and imply that dopaminergic degeneration in the SNc may play an important role in MPTP-induced motor dysfunction of mice.