In present paper is study of an unsteady free convective viscous incompressible flow past a vertical porous flat plate through porous medium with periodic temperature has been discussed in slip-flow regime. Terms involving viscous dissipation have been retained in the energy equation. The temperature of the plate oscillates in time about a constant mean. The analytical expressions for flow characteristics are obtained for variable suction at the porous plate through porous medium. The effect of various parameters on the transient velocity, transient temperature, the skin-friction and rate of heat transfer are discussed with the help of graphs.