PROBLEM TO BE SOLVED: To provide a humanized FcγR mouse.SOLUTION: The present invention relates to: non-human animals in which gene modification includes deficiency of an endogenous low affinity FcγR gene locus, a mouse can exhibit a functional FcR γ-chain, and gene is modified; a method for producing and using the same; and a composition. Described is a mouse whose gene is modified and which includes a functional FcR γ-chain, including a mouse exhibiting low affinity human FcγR gene derived from an endogenous FcγR gene locus. Provided is also a mouse whose gene is modified, and which exhibits low affinity human FcγR genes whose number is up to 5, on an accessory cell of a host immune system.SELECTED DRAWING: Figure 6【課題】ヒト化FcγRマウスの提供。【解決手段】遺伝子改変が内因性低親和性FcγR遺伝子座の欠失を含み、マウスが機能的FcR γ鎖を発現することができる、遺伝子改変された非ヒト動物、ならびにそれらを作製および使用するための方法および組成物を提供する。内因性FcγR遺伝子座由来の低親和性ヒトFcγR遺伝子を発現するマウスを含めた、機能的FcR γ鎖を含む、遺伝子改変されたマウスを記載する。宿主免疫系のアクセサリー細胞上に5つまでの低親和性ヒトFcγR遺伝子を発現する、遺伝子改変されたマウスを提供する。【選択図】図6