A brake disk includes: an outer disk, being substantially ring-shaped and defining a central axis, an inner annular flange of the outer disk formed with connecting bridges, the connecting bridge having a protruding portion disposed through a disposing hole axially; an inner disk, coaxially disposed in the outer disk and located on a same plane with the outer disk, an outer annular flange of the inner disk formed with recessed portions corresponding to the protruding portions respectively, the protruding portion fittingly engaged with the recessed portion to prevent the inner disk from rotating relative to the outer disk, the recessed portion and the protruding portion having a gap therebetween; a plurality of positioning members, each positioning member disposed through the disposing hole to restrain the outer and inner disks from moving relatively axially; wherein the outer and inner disks are axially non-overlapping.