Interleukin (IL)-33 is a recently described member of the IL-1 family and functions as a ligand for ST2, a member of the IL-1 receptor family. The role of IL-33/ST2 axis in the pathogenesis of experimental autoimmune encephalomyelitis (EAE), an experimental model of multiple sclerosis (MS), remains controversial. Matrine (MAT), a quinolizidine alkaloid derived from the herb Radix Sophorae Flave, has been recently found to suppress clinical EAE and CNS inflammation. However, the underlying immunoregulatory mechanisms have not been fully elucidated, and whether this effect of MAT is through inhibiting the function of the IL-33/ST2 axis is not known. In this study, we investigated the relationship between the therapeutic effects of MAT and IL-33/ST2 expression. MAT treatment successfully attenuated severe clinical deficit and histopathological changes, compared to untreated controls. While IL-33/ST2 mRNA expression was largely increased in spinal cord of EAE rats compared to naïve rats, this expression was significantly inhibited in rats treated with MAT. These results were further confirmed by their protein levels tested with immunohistochemistry. Together, our study demonstrates that MAT treatment regulates the inflammatory IL-33/ST2 axis, thus being a novel mechanism underlying the effect of MAT.