We apply the proposed method (NHPSTM) which is the combination of new homotopy
perturbation method and Sumudu transform to solve analytical linear and nonlinear Klein-
Gordon equations. The proposed method finds the solution without any discretization or
restrictive assumptions and avoids the round-off errors. The fact that the proposed technique
solves nonlinear problems without using Adomian’s polynomials can be considered as a clear
advantage of this new method over the decomposition method. Obtained results reveal that
the proposed method is very efficient, simple and can be applied to other nonlinear problems
arising in mathematical physics and engineering.