Disclosed herein is a variable rear spoiler apparatus of a rear bumper for a vehicle. The variable rear spoiler apparatus includes a linkage mechanism configured to be installed on a bumper back beam and having a length varying in a vertical direction when the linkage mechanism undergoes a rotation. A spoiler is connected to the linkage mechanism and is able to move up and down by the rotation of the linkage mechanism. A first driving mechanism, installed at the bumper back beam, is provided with a first rotation shaft connected to the linkage mechanism to transfer a torque. The spoiler is moved up and down by the rotation of the linkage mechanism by a rotation of the first rotation shaft. A second driving mechanism is connected to the first rotation shaft. The spoiler is tilted by a length varying operation of the second driving mechanism.