Passerine birds, especially during the breeding season and nestling development, are exposed to an array of hematophagous ectoparasites. Although the direct consequences of mite infestation on host fitness and immunological function have been investigated in the Domestic Chicken (Gallus gallus domesticus), parasite-specific immune responses to ectoparasites in passerine species have not been examined in great detail. We investigated the humoral immune response of House Sparrows (Passer domesticus) to hematophagous mite antigens and tested for the presence of mite-specific antibodies in adults, egg yolks, and nestlings in a wild population that was naturally exposed to ectoparasitic mites. Our results showed that adult House Sparrows can mount a specific adaptive immune response against hematophagous mite antigens. Further, we demonstrate that mite-specific antibodies are present in wild House Sparrow populations naturally infested with ectoparasites. The results of this study provide ecological immunologists with a tool for examining host-parasite interactions via a parasite-specific immune assay.