In order to obtain a better understanding of the combustion characteristics of ammonium nitrate (AN) and carbon (C) mixtures (AN/C), burning tests and differential scanning calorimetry (DSC) were performed. AN mixed with carbon that is oxidized by nitric acid (HNO3), such as activated carbon (AC), burned at 1MPa. However, AN mixed with carbon that is not oxidized by HNO3, such as graphite, did not burn under 7MPa. Compositions with more than stoichiometric amounts of activated carbon had higher burning rates. Heat characteristic examinations found a similar trend. The burning rate of AN/AC mixed with CuO as a combustion catalyst deteriorated faster than an additive-free one. From the DSC result, AN/AC/CuO had a higher onset temperature and a lower heat of reaction than AN/AC. These results suggested that, in the combustion wave of AN/C, a thermal decomposition zone is formed on the burning surface, and combustion performance was affected by the thermal decomposition of AN/C.