A numerical investigation of impingement heat transfer and fluid flow in a rectangular two-pass duct was carried out. The impingement wall was smooth or with periodically mounted square ribs. A multiblock parallel CFD code was employed for the calculation. The turbulence modeling was treated by applying a low Reynolds number turbulence eddy viscosity model (LEVM) and a V2F model. First, the calculations were validated against available experimental data in a two-pass duct where the impingement wall was smooth. Then, jets impinging on ribbed walls were simulated. The distance from the nozzle to the impingement wall was fixed at four nozzle diameters (d). The square rib width was set as 0.5 d. The duct inlet Reynolds number was fixed at 10,000. Results show that the presence of ribs was favorable for the heat transfer enhancement on the impingement wall, but not for the side wall.