In this work, we present (G'/G,1/G)-expansion method for solving fractional differential equations based on a fractional complex transform. We apply this method for solving space-time fractional Cahn-Allen equation and space-time fractional Klein-Gordon equation. The fractional derivatives are described in the sense of modified Riemann-Lioville. As a result of some exact solution in the form of hyperbolic, trigonometric and rational solutions are deduced. The obtained solutions may be used for explaining of some physical problems. The (G'/G,1/G)-expansion method has a wider applicability for nonlinear equations. We have verified all the obtained solutions with the aid of Maple.