An analytical solution to the problem of an MHD oscillatory free convective Poiseuille flow through a porous medium with first order chemical reaction is presented. A magnetic field of uniform strength is assumed to be applied normal to the plates. The governing equations are solved by regular perturbation technique. The expressions for velocity, temperature and concentration fields, skin frictions at the plates, the coefficient of the rate of heat transfer from the plates to the fluid, the coefficients of rate of mass transfer at the plates are obtained in non- dimensional form and the effects of the different physical parameters involved in the problem on these fields are discussed graphically and the results are physically interpreted.