In this paper, a decoupled backstepping sliding mode control method is proposed to control underactuated systems under uncertainties and disturbances. The slidingmode control technique and the backstepping control technique are combined owing to their merits. Since the design methodology is based on the Lyapunov theorem, the stability of the system is guaranteed. The effectiveness of the proposed method is verified by the experimental results of the controller which is applied to a nonlinear, underactuated inverted pendulum system. The experimental results show that the decoupled backstepping sliding mode control achieves a satisfactory control performance rather than the decoupled sliding mode controller and the proposed method provides a robust performance to overcome parametric uncertainties where the decoupled sliding mode control fails.