There is a growing need to discuss the solution behavior of fractional differential equations (FDEs), the analytic solutions of the most FDEs generally cannot be obtained. As a consequence, approximate and numerical techniques are playing an important rule in identifying the solutions behavior of such fractional equations and exploring their applications. There are many versions of denitions for fractional derivatives, and integrals. We mention here the formal denition (Riemann-iouville), its modifed form (Caputo) and Grunwald-Letnikov's denition.