In a vehicle steering system, when a sensor malfunction determination unit detects a malfunction of a rotation angle sensor, the sensor malfunction determination unit changes a control mode from a first control mode to a second control mode. In the second control mode, an actual rotor angle (mechanical angle) (θSM) of a steered system motor is computed on the basis of a second rotor angle (electric angle) (θSE2) estimated by a rotation angle estimation unit. Then, feedback control is executed such that the actual rotor angle (θSM) converges to a target rotor angle (θSM1*) that is obtained by superimposing a rotation maintaining command signal on a target rotor angle (θSM*) computed by a target rotor angle computation unit.