This paper presents an adaptive sliding-mode observer for, speed-sensorless field-oriented control of induction motors, The observer detects the rotor flux components in the two-phase :stationary reference frame by the motor electrical equations. The motor speed is estimated by an additional relation obtained by a Lyapunov function. The analytical development of the sliding observer and the speed estimation algorithm is fully: explained. Experimental results are presented, based on a TMS320F240 digital signal processor controller implementation. The system performance with different observer gains and the influence of: the motor parameters deviations are shown and discussed.