The effect of RDX addition on the combustion wave structure of double-base propellants has been examined in order to understand the burning rate characteristics of RDX-CMDB (composite modified double-base) propellants and to extend the burning rate domain of double-base propellants, RDX was used in this study as the energetic material and also the agent to decrease the burning rate of doublebase propellants. Experiments were conducted to determine the temperature profile in the combustion waves by means of fine thermocouples, It was found that the reaction rate in the fizz zone is decreased by the addition of RDX. This is caused by the equivalence ratio in the fizz zone becoming fuel rich when RDX is added. The reduction of the reaction rate in the fizz zone decreases the heat feedback from the gas phase to the burning surface. Thus, the burning rate of RDX-CMDB propellants decreases when RDX is added to double-base propellants.