An analysis is made for the study of unsteady MHD free convection flow of a viscous, incompressible, electrically conducting fluid past a semi-infinite porous vertical plate in the presence of thermal radiation. A uniform transverse magnetic field is applied normal to the plate.  The governing equations are solved by perturbation technique. The expressions for the velocity field, temperature field and concentration field are obtained in non-dimensional form. The effects of the various physical parameters like magnetic field parameter, Schmidt number, Prandtl number, heat sink parameter, chemical reaction parameter, radiation parameter and Soret number on these fields are discussed through graphs and tables.

heat and mass transfer, thermal diffusion, Nusselt number, Sherwood number, suction, heat sink.