The disturbance attenuation and rejection problem is investigated for a class of MIMO systems subject to disturbances. The disturbances are supposed to include two parts. One in the input channel is generated by an exogenous system with uncertainty, which can represent the harmonic signals with modeling perturbations. The other is supposed to have the bounded H₂ norm. The disturbance observers are proposed, which can be constructed separately from the controller design. A novel type of control scheme combined the disturbance-observer-based control (DOBC) with discrete-time sliding mode control (DSMC) is presented for a class of MIMO systems. By integrating DOBC with DSMC laws, the disturbances can be estimated and attenuated, simultaneously, the desired dynamic performances can be guaranteed. Simulations for a flight control system are given to demonstrate the effectiveness of the results compared with the previous schemes.