Three-component velocity distributions in a rocket-ramjet combined cycle engine model operating under a sea-level static condition were measured with a stereoscopic particle image velocimetry. The engine model had two rocket nozzles on top wall side of a flow-path and fuel injectors for the secondary combustion. The rocket exhaust was simulated by the cold compressed air injected at operation condition of 2.4 MPa in chamber pressure. The secondary fuel was simulated by the helium gas. The pressure rise due to combustion was simulated by contracting the exit area of flow path by using a flow plug. The separation region appeared in the cowl side in the ensemble-averaged velocity distribution in the case of combustion simulation. The flow around the separation region was strongly disturbed.