An inside mirror assembly for a vehicle may include a housing which has an opening portion formed at a front side thereof, a fixed reflective plate which is fixed and mounted to the opening portion of the housing, a tilting reflective plate which is tiltably mounted in the housing, and disposed parallel to a rear surface of the fixed reflective plate in a day reflective mode, or disposed so that an upper end portion of the tilting reflective plate is tiltable rearward at a predetermined angle on a basis of a lower end portion of the tilting reflective plate in order to reduce light reflectivity in a night reflective mode, and a tilting operation mechanism which is connected with the tilting reflective plate, mounted inside and outside of the housing, and adjusts a tilting angle of the tilting reflective plate.