An experimental study was conducted to investigate the performances of an ejector-jet, which will be used from takeoff to low supersonic flight speed. The supersonic primary rocket exhaust was simulated by air. The secondary air flow was simulated by nitrogen. The total pressure ratio of the secondary flow to the primary flow, the entrance area ratio of the secondary flow to the primary flow, and Mach number of the primary flow at the entrance were changed. The Mach number of the primary flow was 2.4 or 3.4. The effect of combustion was simulated by the downstream choking. One and two-dimensional model calculations were conducted. The experimental results were comparable to the model results. These models were effective for design of the ejector-jet.