The thermal decomposition behavior and combustion characteristics of mixtures of ammonium dinitramide (ADN) with additives were studied. Micrometer-sized particles of Al, Fe2O3, TiO2, NiO, Cu(OH)NO3, copper, CuO, and nanometer-sized particles of aluminum (Alex) and CuO (nano-CuO) were employed. The thermal decomposition was measured by TG-DTA and DSC. The copper compounds and NiO lowered the onset temperature of ADN decomposition. The heat value of ADN with Alex was larger than that of pure ADN in closed conditions. The burning rates and temperature of the pure ADN and ADN/additives mixtures were measured. CuO and NiO enhance the burning rate, particularly at pressures lower than 1 MPa, because of the catalyzed decomposition in the condensed phase; the other additives lower the burning rate. This negative effect on the burning rate is explained based on the surface temperature measurements by a physicochemical mechanism, which involves a chemical reaction, a phase change of the ammonium nitrate, and the blown-off droplets of the condensed phase.