A bicycle disc brake hub is basically provided with a hub axle and a hub shell rotatably disposed about the hub axle. The hub shell has a pair of flanges with a tubular portion extending between the flanges, and a rotor attachment portion configured to prevent an inside diameter of a disc brake rotor from increasing when the diameter of the hub axle increases. The rotor attachment portion is provided in the vicinity of a first shell end of the hub shell, and has a smaller outside diameter than the outside diameter of the tubular portion. A rotor of a disc brake device is attached to the rotor attachment portion.