Product studies were performed to elucidate degradation pathways of MTBE, ETBE, TAME, and di-isopropyl ether (DIPE) under the irradiation of ultrasound. The major intermediates, acetone, tert-butyl alcohol, tert-butyl formate, and methyl acetate were identified by GC-MS and monitored by purge & trap GC. Formaldehyde was determined by Hantzsch reaction. DIPE was decomposed quite rapidly producing intermediates, isopropyl acetate, acetone, and acetaldehyde. ETBE and TAME have more reactive sites to be reacted and produced more complicated product mixtures, including tert-butyl acetate, acetone, tert-butyl alcohol, ethyl tert-butyl acetate, and tert-butyl formate from ETBE; acetaldehyde, acetone, methyl acetate, butanone, methyl propionate, tert-amyl alcohol and tert-amyl formate from TAME. Pyrolytic degradation of C-C bond or abstraction of α- (or β-) hydrogen by ·OH led to a carbon centered radical, which could react with oxygen molecule to give the peroxyl radical, ROO·.