An investigation is made to carry out to study the thermal diffusion and diffusion thermo effects in hydro magnetic transient flow by a mixed convection boundary layer past an impermeable vertical stretching sheet embedded in a conducting fluid saturated porous medium in the presence of a chemical reaction effect. The velocity of stretching surface, the surface temperature and the concentration are directly proportional to the distance along the surface. The flow is impulsively set into motion rest, and both the temperature and concentration at the surface are also suddenly changed from that of the ambient fluid. An external magnetic field of strength is applied perpendicular to the stretching sheet. Introducing non dimensional parameters, the governing set of partial differential equation are transformed into the self similar unsteady boundary layer equations. These equations are solved by Runge kutta integration scheme with shooting method for the whole transient flow from initial state to final steady state flow. Numerical results for the velocity, temperature, and Concentration profiles are presented graphically for different existing flow parameter. A special case of our results is in good agreement with an earlier published work.