An analysis has been carried out to obtain the free convective heat and mass transfer characteristics of an incompressible MHD viscoelastic fluid flow immersed in a porous medium of variable permeability bounded by an infinite porous vertical plate in slip flow regime in the presence of a transverse magnetic field with heat source and radiation effects. The permeability of the porous medium decreases exponentially with time about a constant mean. Approximate solutions have been obtained for the velocity, temperature, concentration, skin friction and rate of heat transfer. The numerical results are displayed graphically to study the effect of several pertinent parameters such as viscoelasticity, permeability of the porous medium, magnetic field, Grashof number, modified Grashof number, Schmidt number, Prandtl number, radiation parameter, heat source/sink parameter and rarefaction parameter on the flow, heat and mass transfer characteristics. The numerical results of velocity distribution of viscoelastic fluid are compared with the corresponding flow problems for a viscous fluid.