An experimental study on a reattaching separated flow over a backward facing step with a nitrogen gas injection from a slit port to the recirculating zone has been conducted by means of flow measurement and visualization. The mean velocity, the turbulent intensity obtained from the fluctuating velocity in streamwise and cross-stream direction and the Reynolds shear stress have been measured using a laser Doppler velocimeter. A laser-sheet based visualization has been made to demonstrate the complex nature of the flow field. In the experiments, the free stream velocity was kept constant at 10 m/s and the specific momentum ratio between the injected gas and main airflow was varied by changing the injection velocity. Two cases of injection location have been investigated, one at a near step and another one at a near reattachment location. The profiles of measured turbulent properties show that as the specific momentum ratio of the injection is increased, the turbulent intensity and the Reynolds shear stress increase in the shear layer region, while they tend to decrease in the reverse flow zone. These effects are more pronounced in case of the gas is injected at the near step location. Further assessment on recorded images suggest that changing the specific momentum of injection alters the injected jet behavior with respect with its fluctuation, mixing with the airflow as well as the dimensionality of its growth.