This paper proposes the control design for the wheeled mobile robot in the presence of external disturbances, parametric uncertainties together with input saturation. Integrating the extended state observer technique, a practical method named sliding mode control is designed to force the state variables to attain the stable equilibrium with the help of extended state observer by compensating uncertainty and disturbance (called lumped uncertainty). To handle the shortcoming of undesired chattering and the difficulty of choosing the control gain, sliding mode control with adaptive mechanism is applied, which has the ability to automatically adjust the control gain and can even work well without a requirement of knowing the upper bound on lumped uncertainty. Subsequently, an auxiliary system is further developed to cope with input saturation problem. In addition, the stability analysis of the closed-loop system is rigorously proved via Lyapunov theorem, manifesting that the proposed controller can guarantee the ultimate boundedness of all signals in the overall system and make tracking errors converge to an arbitrarily small neighborhood around zero by selecting appropriate control parameters. Finally, simulation results are intuitively carried out to demonstrate the feasibility of the introduced adaptive composite controller.