Experimental autoimmune encephalomyelitis (EAE) is an inflammatory demyelinating disease of the central nerve system that is considered a T helper type 1 (Th1)-mediated autoimmune disease. EAE currently serves as an experimental animal model for multiple sclerosis in human. Cytokines, such as interferon-γ and interleukin-10, play a key role in the development and remission of EAE. Recent studies have also shown a role for B cells in the pathogenesis of EAE. Therefore, we examined the role of CD19, a B cell-specific surface molecule that defines signaling thresholds critical for B-cell responses and autoimmunity, on the development of EAE. Following immunization with myelin oligodendrocyte glycoprotein (MOG) peptide, CD19-deficient (CD19^−/−) mice exhibited higher clinical and pathological severity scores of EAE than wild-type mice. The increased severity of EAE in CD19^−/− mice was associated with polarized Th1 cytokines in the inflamed central nerve system but not with anti-MOG antibodies in the serum. MOG-primed CD19^−/− B cells produced high levels of interferon-γ, and transfer of MOG-primed CD19^−/− B cells to wild-type mice worsened the disease. Thus, CD19 modulates the Th1/Th2 cytokine balance in B cells and plays a critical role as a suppressive molecule in the development of EAE.