This paper presents a sliding mode control using only output information. The robustness conditions come from a linear matrix inequality (LMI). This LMI permits to use output feedback to stabilize the system with matched and unmatched disturbances and uncertainties. The controller synthesized consists of two components. One component of linear output feedback regulates the system and rejects the unmatched disturbance. Other components of nonlinear output function provide robustness to the overall system. Robustness conditions are given. Simulations results using Simulink Matlab to simulate several nonlinear systems are presented