A diacyltaurolipid was found in cells of Tetrahymena mimbres (formerly Tetrahymenas pyriformis NT-1). The lipid accounted for about 0.05% of the total lipids of the cells, and was composed of taurine (1 equiv.), 3,7,13-trihydroxystearic acid (1 equiv.) and non-hydroxy fatty acids (2 equiv.). By mild alkaline hydrolysis, non-hydroxy fatty acids (2 equiv.) and 2-(3,7,13-trihydroxyoctadecanoyl)aminoethanesulfonic acid were obtained. For determination of the positions of the ester bonds of the lipid, the free hydroxy group of the intact lipid was converted to a ketone, and the esterified hydroxy groups were acetylated after methanolic hydrochloric acid hydrolysis. By mass and nuclear magnetic resonance spectrometry, the structure of the derivative was identified as methyl 3,7-diacetoxy-13-oxooctadecanoate. From these results, the diacyltaurolipid isolated from T. mimbres was identified as 2-(3,7-diacyloxy-13-hydroxyoctadecanoyl)aminoethanesulfonic acid (7-acyltaurolipid A). This structure suggests that the diacyltaurolipid may be formed by acylation of taurolipid A.