Abstract: In this study, we investigate angle control by active disturbance rejection for an inverted-pendulum system under complex conditions. We define the periodic disturbances, model uncertainties, and backlash hysteresis that occur in practical mechanical systems as input disturbances of the control system. Then, we use the extended state to model and estimate the input disturbance, and achieve angle control for an inverted pendulum under complex conditions by designing an extended state observer and state feedback. Lastly, we conduct simulations and experiments on single inverted pendulums. The experimental results indicate that three kinds of influence factors were weakened by the proposed active-disturbance-rejection angle control method with good control performance.