Abstract: This study presents an approximate solution to a 3-dimensional free convection flow of a viscous, incompressible fluid past an impulsively started infinite, vertical porous limiting surface through porous medium with transverse sinusoidal suction in presence of uniform magnetic field. Using perturbation technique, the expressions for the transient velocity in the main flow direction, the temperature, the sinusoidal skin fraction and the rate of heat transfer have been discussed with there respective dependence on the Prandtl number (Pr), Grashoff number (Gr), Magnetic parameter (M) and Porosity parameter (K).