This study investigates the role of microRNA-155 (miR-155) in autoimmune inflammation. *Mir155*^−/−^ mice were found to be highly resistant to experimental autoimmune encephalomyelitis (EAE), a model of autoimmune inflammation. MiR-155 functions in hematopoietic cells to promote the development of inflammatory T cells, including T helper 17 (Th17) and Th1 cells. The major contribution of miR-155 to EAE was found to be intrinsic to CD4+ T cells, although it also required for optimal dendritic cell production of cytokines that promote Th17 cell formation. These findings suggest that miR-155 plays a crucial role in promoting T cell-dependent tissue inflammation and could be a promising therapeutic target for autoimmune disorders.This study investigates the role of microRNA-155 (miR-155) in autoimmune inflammation. *Mir155*^−/−^ mice were found to be highly resistant to experimental autoimmune encephalomyelitis (EAE), a model of autoimmune inflammation. MiR-155 functions in hematopoietic cells to promote the development of inflammatory T cells, including T helper 17 (Th17) and Th1 cells. The major contribution of miR-155 to EAE was found to be intrinsic to CD4+ T cells, although it also required for optimal dendritic cell production of cytokines that promote Th17 cell formation. These findings suggest that miR-155 plays a crucial role in promoting T cell-dependent tissue inflammation and could be a promising therapeutic target for autoimmune disorders.