This paper deals with the problem of output feedback sliding mode control for sampled-data systems in the presence of external disturbances. A discrete-time high gain output feedback control strategy is proposed to achieve a quasi sliding mode with an Ο(T3) boundary layer, where T is the sampling period. This new control strategy enables an Ο(T 2) bound for state regulation, which outperforms the Ο(T) result induced by the one-step-ahead disturbance approximation method. The analysis of stability and robustness of the closed-loop system is carried out with the help of the singular perturbation technique. A numerical example of an aircraft attitude output feedback control problem is given to illustrate the efficacy of the new method.