<p>This paper presents an observer for estimating unknown disturbances and a novel disturbance rejection tube model predictive controller for nonlinear systems to enhance control performance. The proposed robust control framework comprises two components: a disturbance rejection controller designed using disturbance estimation and a tube-based MPC to address residual disturbances. First, a state and disturbance observer is developed to estimate the disturbance information based on the system output. Next, the estimated disturbance information is utilized to design a disturbance rejection controller to counteract matched disturbances. Subsequently, to mitigate the effects of the residual disturbances, a tube-based MPC is formulated to improve the robustness of the nonlinear system. Finally, the recursive feasibility and system stability of the closed-loop system are rigorously analyzed, and the effectiveness of the proposed method is validated through simulations in a continuous stirred tank reactor (CSTR) system.</p>