Eosinophils are multifunctional leukocytes that reside in several tissues, most abundantly in the small intestinal lamina propria under the steady state. To date, the phenotypic and functional characteristics of small intestinal eosinophils have remained poorly understood. In this study, we found that proliferation of ovalbumin (OVA)-specific CD4+ T cells isolated from the mesenteric lymph nodes of eosinophil-deficient DeltadblGATA mice were decreased relative to wild-type mice after oral immunization with OVA and cholera toxin (CT), the typical mucosal adjuvant that induces CD4+ T cell-dependent responses. DeltadblGATA mice showed reduced mucosal secretion of OVA-specific IgA and IgG1 while maintaining a systemic level of anti-OVA IgG1 upon oral immunization with OVA and CT. These findings suggest that eosinophils might have a role in the modulation of T cell-mediated immune responses including mucosal antibody responses in the gastrointestinal tract following oral immunization.