This paper considers the three dimensional mixed convective MHD flow and heat transfer of a viscous incompressible electrically conducting fluid through a highly porous medium bounded by an infinite vertical porous plate with periodic permeability. The main objective of this study is to analyze the effect of periodic permeability and applied magnetic field on the flow field through a highly porous medium bounded by an infinite vertical porous plate. Assuming the free stream velocity to be uniform, the governing equations are solved and approximate solutions are obtained for the velocity field, the temperature field, the skin friction and the heat flux in terms of Nusselt number (Nu). The effects of the flow parameters characterizing the flow field are studied and discussed with the help of figures and tables.