In this paper, a novel sensorless nonlinear speed control for a permanent magnet synchronous motor (PMSM) driving an unknown load torque is developed and integrated with the vector control scheme. An extended nonlinear state observer with parameter adaptive scheme is used to estimate the states of the motor and disturbance torque avoiding the use of mechanical sensors. The parameter identified adaptively is stator resistance which varies with motor temperature and frequency. Furthermore, to improve the performance of the speed controller the load inertia is identified by the periodic test signal. The proposed sensorless makes the drive system accurate, robust and insensitive to parameter variation. The steady state and dynamic performances of the proposed sensorless drive using digital simulation results are demonstrated.