This paper presents an exact solution to study chemical reaction, diffusion-thermo (Dufour effect) and radiation effects on unsteady MHD free convective heat and mass transfer flow past an impulsively started infinite vertical plate with variable mass diffusion in the presence of applied transverse magnetic field. Initially, it is assumed that the plate and surrounding fluid are maintaining a temperature T′ ∞ in stationary condition with concentration levels C′ ∞ at all the points in entire flow region. At time t > 0, the plate is given an impulsive motion moving with a uniform velocity u0. And at the same time, the plate temperature is raised to T′ w and the level of concentration near the plate is raised linearly with time t. The dimensionless governing equations involved in the present analysis are solved using the Laplace transform technique. Non-dimensional velocity, temperature and concentration profiles are then presented graphically for different values of parameters entering into the problem while the numerical computations of skin-friction are presented in a tabular form. © 2013 Pushpa Publishing House.