A theoretical development of output-sliding control for uncertain mismatched multivariable systems is presented. The control law consists of a continuous nominal control part and a discontinuous switching control part. The determination of controller gains is explicit and practical. The closed-loop eigenvalues assignment in the sliding mode is well addressed. System robustness against a larger class of parameter variations and disturbances than by conventional design methods is achieved. Simultation studies show the promise of the proposed method.