The relation between burning rate and pressure was obtained for the monopropellant HNIW with some metal oxides and organometallic salts added. It was found that PbO, Fe2O3, CuO, etc. did not decrease the exponent for the dependence of burning rate on pressure; but some organometallic salts did. The combustion characteristics of HTPB/HNIW composite solid propellants were also studied. Photographs of the flame structure of HNIW propellants were taken. The thermal decomposition of these propellants with organometallic salts added were studied using DSC and in situ FTIR. Some additives inhibit the thermal decomposition of HNIW. (C) 2003 The Combustion Institute. All rights reserved.