A vitiated-air heater for test facilities of air-breathing engines was developed. We adopted a coaxial injector as the burner element. Coaxial injectors were popularly used for the GH(2)-LO2 rocket engines. For gaseous mixtures, however, coaxial injectors had defects, such as less flame stability and insufficient mixing characteristics due to its high injection speed. Two types of model burners on a small scale were used in the experiment. Hydrogen was used as the fuel and air, containing an adequate amount of oxygen as the oxidizer. One is a burner with one injector (one-element burner). This type was used to obtain the fundamental combustion characteristics, such as combustion stability limits, the relationship between air and fuel injection velocities and so on. The other is a four-element burner, which has four injectors in the combustion region and eight dilution air injectors in the space enclosed by the liner and the combustion chamber inner wall. This second model is used to obtain burner characteristics, such as exit gas temperature profiles. The experimental results showed that stable combustion, uniform profiles of burner exit gas temperature and high heat release rates were attainable with the developed air heater.