ObjectiveTo study the pathological and immunological changes of chronic dermatitis in KM mutant mice. MethodThe changes of external characteristics were observed by stereomicroscopy and optical microscopy, and the immune cells and inflammatory factors were observed using HE staining, immunohistochemistry and toluidine blue staining in 3-, 6-month old wild-type and KM mutant mice. ResultsThe skin changes showed oligotrichia, scurf, rhicnosis and the histopathology showed epidermal cell necrosis, epithelial hyperkeratosis or parakeratosis, hypergranulosis, basal cell layer edema, dilatation of blood vessels in the superficial layer of dermis and infiltration of inflammation cells in the connective tissue; increase of cutaneous CD3+ and CD4⁺T cells, macrophages and mast cells; and increase of inflammatory factors IL-6, IL-22, TNF-α, and IFN-γ in the 6-month old KM mutant mice and more severe in the 3-month old KM mutant mice . ConclusionsThe skin tissue of KM mutant mice shows chronic inflammatory changes in pathology and cell-molecular changes similar to that in human chronic inflammatory skin diseases. KM spontaneous mutant mice may become a novel animal model in research of of chronic dermatitis .