Multiple sclerosis (MS) is an autoimmune disease characterized by demyelination, axonal damage and progressive neurologic dysfunction in central nervous system (CNS). Many evidences show that B cells play an important role in the pathogenesis of MS. Follicular helper T cells (Tfh) secrete IL-21 to prompt the proliferation and differentiation of B cells in germinal center (GC) through clonal proliferation, somatic hypermutation, antibody class switching, antibody affinity maturation process. AG490 is a synthetic inhibitor to JAK-STAT signal pathway, which has been studied in inflammatory, tumor and autoimmune diseases. In the present study, the experimental mice were divided into 3 groups, vehicle group and AG490 group were given MOG35-55 to induce EAE model, from the third day after immunization, the mice were given vehicle or AG490 by intraperitoneal injection every other day. All mice were assessed clinical scores after immunization. On twentieth day, all mice were sacrificed, HE staining and solochrome cyanine staining were performed to evaluate inflammatory cells infiltration and demyelination, spleen sections were stained with PNA-FITC to analyze the difference in germinal center. Compared with vehicle group, the incidence of AG490 group was deceased, onset time was delayed, the severity was significantly reduced. The inflammatory cells and demyelination in AG490 group were lower than those in vehicle group. Immunofluorescence showed the fluorescence intensity of AG490 group was significantly lower than in the vehicle group, but higher than that of control group.