Highly pure ethyl oleate and ethyl elaidate were ozonized to their secondary ozonides (respectively EO-SOZ and EE-SOZ). The decomposition enthalpies of EO-SOZ and EE-SOZ were determined by DSC (Differential Scanning Calorimetry) and found, respectively, at -266 kJ/mol and -264 kJ/mol, a value much closer to the theoretically calculated upper limit of -278 kJ/mol than the decomposition enthalpy of -243 kJ/mol measured on EO-SOZ prepared from an ethyl oleate sample conforming to the European Pharmacopoeia. Although a considerable amount of heat was liberated, EO-SOZ and EE-SOZ cannot be defined as explosive based on their DSC traces at a heating rate of 10 • C/min. Pure EO-SOZ and EE-SOZ show a decomposition peak at the DSCs of 137 • C and 139 • C, respectively. The thermal decomposition of EO-SOZ and EE-SOZ was studied also by FT-IR spectroscopy showing that the decomposition involves the loss of the ozonide infrared band at 1110 cm −1 and the formation of the expected decomposition products (pelargonic acid, pelargonaldehyde, ethyl azelate, etc.). The kinetics of the photochemical decomposition of EO-SOZ and EE-SOZ were studied by FT-IR spectroscopy, and the relative rate constants were determined. EO-SOZ when overozonized forms a spin adduct with nitrosobenzene and the relative nitroxyl radical was clearly detected by the Electron Spin Resonance (ESR). Secondary ozonation products known as trioxides may be responsible for these adducts.