An adjustable rail-hanging apparatus comprises a main body and a limit device, wherein a hooking part for hooking an aluminum extrusion hanging board is mounted on the upper end of the main body. First screw holes to be inserted by first locking devices are formed on both sides of the main body and guiding grooves are oppositely formed on both sides of the lower end of the main body respectively for movably holding the limit device. A hooking notch is formed on each holding part of the limit device. The adjustable limit device is movably shifted up and down by disposing second locking devices in the guiding grooves and holding the aluminum extrusion hanging board by the hooking notch and the hooking part on the upper end of the main body cooperatively. Consequently, the movable limit device is suitable for aluminum extrusion hanging board with various rail gauges.