This paper proposes a systematic methodology for designing robust static output feedback sliding mode control (SOFSMC) for a class of systems with mismatched uncertainties. This methodology consists of two parts: one is a new sufficient and necessary condition for the existence problem in terms of two matrix inequalities; the other is a direct solving method using the iterative linear matrix inequality (ILMI) technique. The main advantages of this method are that only original system parameters are involved without any extra coordinate changes, and that appealing to solving the static output feedback stabilization (SOFS) problem is no longer required. In addition, the ILMI algorithm includes an optimal part to avoid high control efforts. A numerical example also demonstrates the efficacy of the proposed approach.