Abstract: An active disturbance rejection control (ADRC) scheme is proposed in this paper for the attitude control problem of dynamic processes with liquid sloshing, which is characterized by poor dynamic stability, rapid parameter variations, and significant uncertainties. Simulation results verify that the scheme can effectively suppress the influence of disturbances and liquid sloshing on attitude motion, and exhibits strong adaptability to different tank fill ratios as well as uncertainties in disturbances and parameters. Further analysis of the eigenvalues of the closed-loop system reveals the characteristic of ADRC: by effectively compensating online for various disturbances in attitude motion, the rigid body part is approximately restored to a second-order linear time-invariant pure integral object. As a result, the closed-loop characteristic roots related to the attitude part are stable and have similar magnitudes at different characteristic points during the propellant consumption process. Therefore, a satisfactory attitude control effect can be achieved, when liquid sloshing is present. Finally, taking this problem as an example, the issue of how to evaluate the stability margins of nonlinear or linear time-varying systems is discussed.