IL-17A is known to be involved in the host defense against pathogens and pathogenesis of autoimmune diseases. Previously, we showed that excessive IFN-γ plays an important role in the pathogenesis of lethal effect of Toxoplasma gondii (T. gondii) by inducing anaphylactic responses. In this report, we examine the effects of an IL-17A deficiency on murine host defense against oral T. gondiiinfection. IL-17A-deficient C57BL/6 (B6) mice exhibited higher mortality than wild type (WT) mice to T. gondii at the acute phase of infection. CD4+ T cells in mesenteric lymph nodes (mLNs) and ileum of T. gondii-infected IL-17A-deficient mice produced higher levels of IFN-γ than did those in WT mice. In addition, T. gondii HSP70 (T.g.HSP70) expression was also significantly increased in the ileum, mLNs, liver and spleen of infected IL-17A-deficient mice as compared with WT mice. These elevated expressions of T.g.HSP70 and IFN-γ in infected IL-17A-deficient mice were presumably linked to the IL-17A defect since they decreased to WT levels after treatment with recombinant IL-17A. Furthermore, IL-17A-deficient mice were highly susceptible to anaphylactic effect of T.g.HSP70, and acute phase survival of IL-17A-deficient mice was improved by the treatment with anti-T.g.HSP70 monoclonal antibody. These results suggest that IL-17A plays an important role in host survival against T. gondii infection by protecting host from anaphylactic reaction via downregulating T.g.HSP70 and IFN-γ production.