An isothermal permeable plate is assumed to be immersed vertically in a homogeneous viscous electrically conducting fluid containing a concentration species and a magnetic field is applied transverse to the plate. Assuming fluid viscosity to be an inverse linear function of temperature and taking into consideration Ohmic heating, double diffusive Magnetohydrodynamic (MHD) free convective flow and heat transfer at the plate is studied numerically. Assuming the flow to be two-dimensional and introducing a similarity variable, the governing equations of the problem are reduced to a set of non-linear ordinary differential equations. The equations subject to appropriate boundary conditions are solved by Nachtsheim-Swigert scheme together with a shooting technique. Taking into consideration both aiding and opposing buoyancies, the effects of magnetic field, Ohmic heating, mass diffusion and chemical reaction on different flow and heat transfer characteristics like Skin friction, Nusselt number, Sherwood number are presented and discussed. For assisting buoyancies skin friction and Nusselt number are found to diminish with increasing Schmidt number while, for opposing buoyancies, they are found to increase with increasing Schmidt number. In both the cases of assisting and opposing buoyancies, Sherwood number is an increasing function of Schmidt number.