In this article, the multistage homotopy perturbation method (MHPM) is applied for solving differential systems with fractional order derivatives in the Caputo sense. This method is a modification of the standard homotopy perturbation method (HPM). A fractional Lorenz system as an application is presented for which some numerical comparisons between the (MHPM) and (HPM) with the 4th order Runge-Kutta method (RK4). The results reveal that the used pre-mentioned procedure (MHPM) is a reliable and an effective tool for constructing an accurate approximate solution for the fractional Lorenz system.