Increasing evidence suggests that inflammation may be involved in the loss of dopaminergic neurons in Parkinson's disease (PD). Among inflammatory molecules, COX-2, a key kinase for the inflammatory response, has been suggested to play an important role in dopaminergic neuron loss in PD. However, the upstream molecular pathways of COX-2 expression remain uncertain. In the present study, we investigated the role of c-Jun [1] N-terminal kinase (JNK) in the process of COX-2 expression in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of subacute PD. Our data showed that MPTP induced a transient JNK activation of dopaminergic neurons, upregulated COX-2 expression in dopaminergic neurons, and caused the loss of dopaminergic neurons. We found that inhibiting JNK with SP600125, a special inhibitor of JNK, reduced the levels of c-Jun phosphorylation, blocked p-c-Jun translocation from the cytoplasm to the nucleus in dopaminergic neurons of substantia nigra, mitigated the loss of dopaminergic neurons, and improved motor function in MPTP-induced PD in C57BL/6N mice. These results indicate that JNK signaling pathway may be the major upstream mediator of regulation of COX-2 expression induced by MPTP in vivo and inhibiting JNK activity may represent a new and effective strategy to PD.