The systematic approach of designing a robust sampled-data controller to solve output regulation problem for a MIMO nonlinear systems with unknown external disturbances and varying parameters is presented. The design methodology is based on the construction of two-time-scale motions in the closed-loop system. It has been shown that the proposed dynamical controller with a sufficiently small sampling period induces a two-time-scale separation of the fast and slow modes in the closed-loop system. Stability conditions imposed on the fast and slow modes and small sampling period can ensure that the full-order closed-loop system achieves the desired properties so that the output transient performances are desired and insensitive to parameter variations and external disturbances. Finally, an example with simulation results is presented.