The thermal decompositions of partially ozonized 1,4-cis-polybutadiene (E-BR), 1,4-cis-polyisoprene (E-IR), 1,4-trans-polyisoprene (Z-IR), 1,4-trans-polychloroprene (Z-PCh), and of polybutadiene elastomer (BR) (microstructure : 1,4-cis, 47%; 1,4-trans, 42%; 1,2, 11%) were studied. The respective thermograms were described by the presence of an intense and relatively broad exothermic peak in the 60-200 degrees C range, which is the result of thermolysis of functional groups of the peroxide type. The measured values of the enthalpy of the reaction, normalized with respect to the amount of reacted ozone (kJ/mol O-3), were as follows : 337 (E-BR), 260 (BR), 197 (E-IR), 180 (Z-IR), and 239 (Z-PCh). Values of the activation energy and reaction order were also determined : 122.6, 118.5, 108, 113, 101.5 and 1.0, 0.96, 1.04, 1.08, and 1.25, respectively. The enthalpy values, obtained by means of differential scanning calorimetry, should be used for quantitative determination of ozonides from polydienes and polyisoprenes.