The effects of 3-dodecylsulfanyl-propionic acid 3-(3-dodecyl-sulfanl-propionvioxy)-2,2-bis-(3-dodecylsulfanyl-propionyl-oxy- methyl)-propyl ester (SO), 3,9-bis-octadecyloxy-2,4,8,10-tetraoxa-3.9-diphospha-spiro[5,5]undecane (POf), and 3,9-bis-(2,6-di-tertbutN,1-4-methvl-phenoxy)-2.4,8,10-tetraoxa-3,9-diphospha-spiro[5,5]- undecane (POp), which are used as antioxidants for polymers, on the degradation of nitrocellulose (NC) were investigated under isothermal storage conditions at 393 K with a microcalorimeter. The result indicated that SO/NC and POf/NC accelerated the heat release when compared with NC without an antioxidant, whereas the heat release behavior of NC/POp was similar to that of NC without an antioxidant. In the case of SO/NC and POf/NC, the heat release was observed in the presence of O-2, whereas it was not observed in a N-2, atmosphere. The SO42- content in SO/NC and pO(4)(3)(-) content in POf/NC increased with the storage time. According to this behavior, it can be explained that sulfuric acid or phosphoric acid, which originates from SO or POf, accelerates the autoxidation of NC.