Macrophage migration inhibitory factor (MIF) functions as a pleiotropic protein, participating in inflammatory and immune responses. MIF was originally discovered as a lymphokine involved in delayed hypersensitivity and various macrophage functions, including production of proinflammatory cytokines, glucocorticoid-induced immunomodulator, and natural killer cell inhibitory factor (NKIF), regulation of toll-like receptor expression, adherence and phagocytosis of macrophages, as well as induction of metalloproteinase. Therefore MIF is considered as a potential target protein in many pathophysiological states. In this review, considering the protein structure and the acting mechanisms of MIF, we mainly discuss the important role of MIF in pathogenesis of inflammatory diseases and graft rejection.