Abstract: The surfactant of sodium dialkyl sulfosuccinates was analyzed by fast atom bombardment (FAB) mass spectrometry. Although either positive or negative quasimolecular ions, nM±Na, can be formed in large abundance, there are lacking fragment ions to give valuable structural information about its alkyl group. These sulfosuccinates were transformed first through hydrolysis to corresponding alcohols, and then the products can be identified by normal EI mass spectrometry. So that, the characteristic structure of alkyl group can be obtained. It was shown by above method that the Aerosol MA is sodium di-1-methyipentyl sulfosuccinate, but is not corresponding 2-methylpentyl compound described in literature.