<p>This paper proposes a novel adaptive disturbance observer (ADO)-based global terminal sliding mode control scheme for nonlinear systems subject to matched and mismatched time-varying parameter uncertainties and external disturbances. An ADO is designed such that the estimation errors of the lumped disturbances converge to zero in the finite time. By applying Lyapunov theory, the stability of the closed-loop system is guaranteed and the controlled output approaches to zero in the finite time. A new GTSM control law based on the ADO is developed to alleviate the chattering phenomenon. In addition, the proposed scheme is combined with global SMC to remove the reaching phase which improves the control performance of the system. Using the adaptation laws, the upper bound knowledge of lumped disturbances is not required. Finally, the simulation results demonstrate the validity and feasibility of the proposed scheme.</p>