A novel preclinical mouse model was developed, expressing humanized IL-31, IL-31RA, OSM, and OSMR. This quadruple humanized model showed expression of human cytokines and receptors, validated by functional assays. In an atopic dermatitis model, treatment with nemolizumab reduced scratching frequency, indicating the model’s potential for testing modulators of this pathway preclinically. Additionally, blood and flow cytometric analyses confirmed normal leukocyte and lymphocyte proportions in the humanized mice.