Mecanum-wheeled mobile robots are capable of moving in any direction without changing the heading angle of the robot body. However, due to their nonlinear characteristics and slippage, controlling them requires advanced control methods. Sliding mode control is a powerful control technique that is commonly applied. This controller ensures accurate trajectory tracking in presence of disturbances and uncertainties, while also overcoming limitations of other control methods. In this paper, the authors propose a sliding mode controller combined with a disturbance observer. Although the sliding mode controller provides good robustness against disturbances and uncertainties, it causes chattering phenomenon. The integration of a disturbance observer into it addresses these drawbacks by adapting to the uncertain components and reducing chattering magnitude. Consequently, enabling smoother and more accurate control performance. Numerical simulations with comparisons verify the effectiveness of the proposed controller.