Stabilization of fractional-order nonlinear systems is studied. This paper investigates the problem of global Mittag Leffler stabilization by state and output-feedback for a family of nonlinear Caputo fractional-order systems written in triangular form satisfying linear growth conditions. By using a Lyapunov function, global Mittag-Leffler stability of the closed-loop systems is achieved. Finally, simulation results dealing with a typical bioreactor example are given to illustrate that the proposed design procedures are very efficient and simple.