In this work, we investigated the thermal oxidation of methyl tert-butyl ether (MTBE) using a customer-designed mini-closed-pressure vessel test and quantitatively analyzed the hydroperoxides produced in the primary oxidation via iodimetry. Results showed that MTBE formed high levels of hydroperoxide (5053 ppm) in its autoxidation at 140 degrees C. While the temperature was lower than 110 degrees C, a known condition at which hydroperoxide was undetectable, MTBE maintained stability. One of the hydroperoxides isolated from MTBE oxidation products was identified as 1-tert-butoxymethyl hydroperoxide (TBMHP) according to liquid chromatography mass spectrometry, H-1 and C-13 nuclear magnetic resonance spectroscopy, and Fourier transform infrared spectroscopy analysis. The thermal decomposition of TBMHP was assessed via differential scanning calorimeter (DSC). Results indicated that exothermic onset temperature (T-onset) and thermal decomposition heat (Q(DSC)) of TBMHP were 108.10 degrees C and 1478.05 J.g(-1), respectively. The activation energy of TBMHP with the Kissinger method was 76.23 kJ.mol(-1). Moreover, DSC experiments were employed to study the primary oxidation of MTBE with different equivalence ratios, indicating that primary oxidation temperature (T-0) of MTBE was 208.52 degrees C with the equivalence ratio of 0.05. Increasing the equivalence ratio led to a considerable decrease in T-o.