In this paper, a symmetry classification of a (2 + 1)-nonlinear wave equation u tt − f (u)(u xx + u yy ) = 0 where f (u) is a smooth function on u, using Lie group method, is given. The basic infinitesimal method for calculating symmetry groups is presented, and used to determine the general symmetry group of this (2 + 1)-nonlinear wave equation.