Plumbagin (PL), a herbal compound derived from roots of the medicinal plant Plumbago zeylanica, has been shown to have immunosuppressive properties. Present report describes that PL is a potent novel agent in control of encephalitogenic T cell responses and amelioration of mouse experimental autoimmune encephalomyelitis (EAE), through down-regulation of JAK-STAT pathway. PL was found to selectively inhibit IFN-gamma and IL-17 production by CD4(+) T cells, which was mediated through abrogated phosphorylation of JAK1 and JAK2. Consistent with IFN-gamma and IL-17 reduction was suppressed STAT1/STAT4/T-bet pathway which is critical for Th1 differentiation, as well as STAT3/ROR pathway which is essential for Th17 differentiation. In addition, PL suppressed pro-inflammatory molecules such as iNOS, IFN-gamma and IL-6, accompanied by inhibition of IkappaB degradation as well as NF-kappaB phosphorylation. These data give new insight into the novel immune regulatory mechanism of PL and highlight the great value of this kind of herb compounds in probing the complex cytokine signaling network and novel therapeutic targets for autoimmune diseases.