In this paper we study magnetic field, chemical reaction and viscous dissipation on combined heat and mass transfer over a moving permeable vertical flat plate. A variable magnetic field parallel to the y axis and convective surface boundary condition are applied. The similarity representations of the system of partial differential equations of the problem are obtained via the group method. These similarity equations are then solved numerically by a MATLAB package which uses an implicit finite difference technique. Influences of the various parameters on the velocity, the temperature and the concentration fields across the boundary layer are investigated and numerical results for the velocity, temperature and concentration distributions are shown. The skin-friction factor, the Nusselt number and the Sherwood number are also calculated and displayed in graphs to show the effects of various parameters on them