In this study, electromagnetic scattering from perfectly conducting periodic surface have been solved by means of transformation of problem into equivalent problem, that is scattering from plane represented by high order inhomogeneous inipedance boundary condition (IBC). High order inipedance functions are determined by function of the roughness of the surface. Then, transfonned equivalent problem is solved by means (if series expansion method using Floquet modes. This transformation makes the problem simple formulation and computational effectively without involving calculation of slowly converging periodic Green's function. Results and computational times obtained by transform method and those obtained by Method of Moment (MoM) technique are compared. Good agreements are observed in results. It is also observed that transform method needs much less computational time than MoM method. (C) 2008 Wiley Periodicals, Inc.