A brush seal assembly may include: a packing body configured to be positioned between a rotating body and a fixing body and provided with an insertion groove; a brush seal part configured to include a brush extending toward the rotating body in a state in which one end of the brush seal part is inserted into the insertion groove and a support member supporting the brush; a thermal expansion member configured to adhere to a side of the support member and be thermally expanded in a circumferential direction of the packing body; and a fixing member configured to be fitted in the insertion groove to face the thermal expansion member to simultaneously fix the brush seal part in the circumferential direction and a radial direction of the packing body.