Abstract: The probable molecular structures of PSO3E which came from petroleum sulfoxide were deduced by analyzing IR and GC-MS spectra of PSO3E．According to the IR and GC-MS spectra of PSO3E PSO3E was cyclic sulfoxides．In the light of the interpretation of mass spectra of cyclic sulfoxides and the character of the strongest peak of PSO3E mass spectra PSO3E were a series five-membered cyclic sulfoxides．A series of PSO3E’s ion peaks were found to be C ＋ n H2n－1 CnH2n S ＋OH and CnH ＋ 2n－1S through the interpretating the spectra of PSO3E．The position of substituted radical R was decided according to the peak of ion peaks of CnH2nS ＋OH ．Thus when the value of peak which m／e equals91is larger than that which m／e is77 it was substituted by α-position on the contrary it was substituted by β-position．The analytic results show that PSO3E is a group of isomeric sulfoxides and they are single alkyl sustituted cyclic sulfoxides． 

Key words: petroleum sulfoxide, mass spectrum, structure analysis, composition