Acute kidney injury caused by ischemia-reperfusion injury (IRI) is a major risk factor for chronic kidney disease, which is characterized by renal interstitial fibrosis. However, the molecular mechanisms underlying renal fibrosis induced by IRI are not fully understood. Our results showed that interleukin (IL)−33 was induced markedly after IRI insult, and the kidneys of mice following IRI plus IL-33 treatment presented more severe renal fibrosis compared with mice treated with IRI alone. Therefore, we investigated whether inhibition of IL-33 protects against IRI-induced renal fibrosis. Mice were administrated with soluble ST2 (sST2), a decoy receptor that neutralizes IL-33 activity, or vehicle by intraperitoneal injection for 14 days after IRI challenge. We revealed that mice treated with sST2 exhibited less severe renal dysfunction and fibrosis in response to IRI compared with vehicle-treated mice. Inhibition of IL-33 suppressed bone marrow–derived fibroblast accumulation and myofibroblast formation in the kidneys after IRI stress, which was associated with less expression of extracellular matrix proteins. Furthermore, inhibition of IL-33 also showed a significant reduction of F4/80+ macrophages and CD3+ T cells in the kidneys of mice after IRI treatment. Finally, Treatment with IL-33 inhibitor reduced proinflammatory cytokine and chemokine levels in the kidneys of mice following IRI insult. Taken together, our findings indicate that IL-33 signaling plays a critical role in the pathogenesis of IRI–induced renal fibrosis through regulating myeloid fibroblast accumulation, inflammation cell infiltration, and the expression of proinflammatory cytokines and chemokines.