IL-18, a proinflammatory cytokine, is produced by macrophages, epithelial cells, T cells, neutrophils, NK-T cells, and B cells, and has been implicated in the pathophysiology of a variety of inflammatory diseases including ischemia/reperfusion (IR) injury, transplant rejection, and autoimmune disease. Recent study indicated that neutralization of IL-18 with anti-IL-18 antibody or IL-18-binding protein (IL-18BP) ameliorates IR-induced myocardial injury. However, the mechanism needs to be further investigated. In our current study, syngeneic heterotopic heart transplantation was performed by a modified non-suture cuff technique. We found that IL-18BP treatment ameliorated cardiomyocyte necrosis and infiltration of CD4+ T cells, neutrophils, and macrophages. IL-18BP-treated mice exhibited decreased expression of inflammatory cytokines including IL-1β, IL-23, IL-18, and IL-17. IL-18BP treatment suppressed Th17 differentiation in vivo and in vitro. Adoptive transfer of T cells from IL-18BP-treated mice showed alleviated cardiac IR injury when compared with that transferred from control mice. Furthermore, the decreased infiltration of mononuclear cells and production of troponin T (TnT) induced by IL-18BP treatment were both abrogated by additional administration of recombinant mouse IL-17 (rmIL-17). These data revealed a protective role of IL-18BP in cardiac IR injury. Above all, IL-18BP ameliorates cardiac IR injury in part through suppression of Th17 differentiation.