An exact solution to the unsteady free convection flow past an infinite vertical plate in the presence of mass transfer and periodic heat flux is derived by the Laplace- transform technique. Velocity profiles, penetration distance of the transition point from conduction to convection and the temperature profiles are shown on graphs. The numerical values of the skinfriction and the Nusselt number are listed in Tables. The effects of different parameters like N (buoyancy ratio parameter), omega (frequency), t (time), Sc (Schmidt number) on the flow of air are discussed.