This paper proposes an adaptive speed tracking control scheme for an induction motor subject to unknown load torque via backstepping analysis. The controller is developed under a special nonlinear coordinate transform such that speed control objective can be fulfilled. The underlying design concept is to endow the closed-loop system while lacking the knowledge of some key system parameters, such as the rotor resistance, motor inertia, and motor damping coefficient. The proposed control scheme comes along with a thorough proof derived based on Lyapunov stability theory. Experimental results are also given to validate the effectiveness of the proposed control scheme.