The control of laminar fluid flow and heat transfer characteristics over a backward facing step have been studied by varying location and orientation of a thin adiabatic fin mounted on the top wall. The detailed investigation of geometrical parameters of fin (length, location and orientation) for two different Reynolds numbers is performed numerically and the results are compared to the case without fin. It is found that fin location and orientation can be used to control the primary reattachment point and the peak of local Nusselt number effectively and it acts as a passive controller.