Vector control is one of the most popular control techniques of induction motors. Owing to its simplicity, the indirect vector control gains increasing popularity. This paper proposes a speed sensor-less indirect vector control system of induction motors based on a novel sliding mode control (SMC) speed observer. The observer uses the stator current difference of the estimated value and the actual value to calculate the rotor speed. The simulation results show that the method has a fast response and high accuracy, and it robust to parameter variations.