Abstract: We have reported the first record of an exotic species of mites from an avian host of the order Galliformes in Bastos region, State of São Paulo, Brazil. The new feather mite was identified as Allopsoroptoides galli n. g., n. sp. (Acari: Analgoidea: Psoroptoididae). The hens parasitized by mites had intense itching, desquamation and marked drop in egg production (between 20-30%). Based on the observed signals, this study aimed to verify the influence of parasitism on the blood profile, biochemical and histopathological changes in infested chicks. The infected hens showed hematocrit decrease, leukocytosis and eosinopenia. In serum chemical were observed decrease of alkaline phosphatase (ALP) and creatinokinase (CK) and increase of gama glutamiltransferase enzymes (GGT), cholesterol, and total serum protein. All infected cases had skin lesions such as: hyperkeratosis, inflammatory heterophilic infiltration; hydropic degeneration and mixed cellular infiltration of lymphocytes and plasmocytes. The histopathological observation on the kidney in infected hens showed mild changes such as degeneration of kidney tubules, pyknosis and hemorrhage. The liver of birds infested presented infiltrates of mononuclear cells and vacuolation. It can be concluded that feather mite’s infection causes serious damage to the hens. These results could be really useful to assist diagnosis and prognosis of this infection.