In this article, the new exact travelling wave solutions of the nonlinear space-time fractional Burger's, the nonlinear space-time fractional Telegraph and the nonlinear space-time fractional Fisher equations have been found. Based on a nonlinear fractional complex transformation, certain fractional partial differential equations can be turned into ordinary differential equations of integer order in the sense of the Jumarie's modified Riemann-Liouville derivative. The (G'/G)-expansion method is effective for constructing solutions to the nonlinear fractional equations, and it appears to be easier and more convenient by means of a symbolic computation system. Copyright (C) 2016 John Wiley & Sons, Ltd.