The combustion mechanism of a composite propellant having the nominal composition 84% RDX + 16% HTPB has been investigated experimentally. The following steady combustion parameters were collected over the pressure range 0.1 to 8.21 MPa: burn rates, burn surface temperatures, thermal gradients, heat release in the condensed phase, heat feedback from the gas phase, first and second (or final) flame temperatures. In general, for the tested RDX.HTPB mixture,values smaller than the corresponding AP.HTPB parameters are found, while the burning rate pressure exponent is larger. Likewise, the measured values are smaller than the corresponding pure RDX parameters when HTPB binder is added; a notable exception is the heat release in the condensed phase, which is larger. The obtained dependence of burn rate on burn surface temperature fits the unified gasification law for nitramines. Thus, RDX seems to dictate its macrokinetics law upon the HTPB gasification. The main processes taking place simultaneously at the burn surface are: gasification and thermal decomposition of RDX, as well as oxidation of part of the HTPB binder, probably due to liquid-phase mixing between molten ingredients.