This paper addresses the design of a robust fractional-order dynamic output feedback sliding mode controller (FDOF-SMC) for a general class of uncertain fractional systems subject to saturation element. The control law is composed of two components, one linear and one nonlinear. The linear component corresponds to the fractional-order dynamics of the FDOF-SMC, while the nonlinear component is associated with the switching control algorithm. The closed-loop system exhibits asymptotical stability and the system states approach the sliding surface in a finite time. In order to design the controller, a linear matrix inequality (LMI)-based procedure is also derived. Simulation results demonstrate the feasibility of the FDOF-SMC strategy.