Our previous study showed that the peroxisome proliferator-activated receptor-gamma (PPAR-γ) agonist 15-deoxy-PGJ2 has the promoting ability to differentiate neuronal PC12 cells. To expand our study, the effect of 15-deoxy-PGJ2 on the differentiation of embryonic midbrain cells into dopaminergic neuronal cells was investigated in this study. The relationship between cell differentiation with activation of PPAR-γ and the possible signal pathway were also investigated. 15-Deoxy-PGJ2 increased neurite extension, a typical characteristic of the differentiation of embryonic midbrain cells isolated from 12-day rat embryos in a dose-dependent manner. The expression of differentiation markers, neurofilament, tyrosine hydroxylase, and nestin, was also increased by the treatment of 15-deoxy-PGJ2. Consistent with the increasing effect on cell differentiation, 15-deoxy-PGJ2 increased the expression and transcriptional activity of PPAR-γ in cultured embryonic midbrain cells. In addition, the expression of PPAR-γ and NeuN in the differentiated neuron of fetus (17 days) and adult rat brain was co-localized. Furthermore, treatment of PPAR-γ antagonist bisphenol A diglycidyl ether blocked 15-deoxy-PGJ2-induced neuronal differentiation of embryonic midbrain cells and expression of PPAR-γ. To elucidate the possible signal pathway, the activation of mitogenic-activated protein (MAP) kinase family was determined. 15-Deoxy-PGJ2 (0.5 μM) increased activation of Jun N-terminal kinase (JNK) and p38 kinase but not extra-signal response kinase (ERK). In addition, NGF (50 ng/ml) further increased the 15-deoxy-PGJ2-induced JNK activation. Moreover, pretreatment of specific inhibitor of JNK SP600125 blocked the 15-deoxy-PGJ2-induced JNK activation. This inhibition correlated well with the inhibition of neurite extension and expression of PPAR-γ induced by 15-deoxy-PGJ2. The present results therefore indicate that 15-deoxy-PGJ2 stimulates differentiation of embryonic midbrain cells into dopaminergic neuronal cells, and its effect may be PPAR-γ and JNK signal pathway dependent.