For composite propellants, solid-phase thermal conduction is one of the dominant processes of propellant combustion and influences their burning characteristics. In this study, diatomaceous earth (DE) was used as a low-thermal-conductivity material, and the influence of DE on the burning characteristics of an ammonium perchlorate (AP)-based composite propellant was investigated. The ignitability of the propellant was improved by the addition of DE. DE showed both positive and negative effects on the burning rate of the propellant. The negative effect was attributable to the reduction of energy by the addition of DE. The enhancement in the burning characteristics was attributable to the particle shape and size of DE, the catalytic effect of Fe2O3, and the physical effect of SiO2; Fe2O3 and SiO2 are constituents of DE. The mechanism of the physical effect of SiO2 is as follows. The heat conduction in the solid phase is obstructed by SiO2 particles in the propellant matrix, and the temperature in the vicinity of these particles becomes higher. Consequently, a hot spot is formed on the burning surface side of the SiO2 particles, and the burning rate is then increased. Further, the hot spot effect was dependent on the AP interparticle distance in propellant matrix and the specific surface area of AP. (C) 2013 The Combustion Institute. Published by Elsevier Inc. All rights reserved.