An adjustable neck support includes a neck holder front support, a left side plate, a right side plate, a lower jaw holder plate, and a height adjustment knob. The left side plate is movably connected at a left end of the neck holder front support, the right side plate is movably connected at a right end of the neck holder front support, the lower jaw holder plate is connected between the left side plate and the right side plate, and the height adjustment knob is mounted on the neck holder front support. The height adjustment knob includes an operating cover and a winding post connected to the operating cover, the winding post being mounted in the neck holder front support. The adjustable neck support provided by the application is smooth in height adjustment operation, easy to operate, and long in service life.