The pyrolysis of n-dialkyl peroxides from 150 to 250 °C is a homogeneous reaction controlled by the intial O—O bond fission. When the reaction occurred in an excess of O2 and with a reactant concentration of 100 ppm the reaction sequence was as follows: RCH2O2CH2→ 2RCH2O (1), RCH2O + O2→ RCHO + HO2(2), 2HO2→ H2O2+ O2. (3) The yields of H2O2 and trapped HO2 radicals have been measured. Rate constant values are as follows: (i) for di-n-heptylperoxide log10k1/s–1=(15.00 ± 0.82)–(152.6 ± 9.2) kJ mol–1/2.303 RT for di-n-butyl peroxide log10k1/s–1=(16.02 ± 0.49)–(160.2 ± 10.8) kJ mol–1/2.303 RT. Such values for A and E are in line with those obtained by another method for dimethyl peroxide and di-t-butyl peroxide and are in agreement with empirical correlations. When di-t-butyl peroxide was studied under the same conditions the main radical observed was CH3O2; the main peroxides formed were CH3O2H and H2O2.