1. 1. Phosphatidylethanolamine from St. sioyaensis afforded a double spot on a thin-layer chromatogram, typical of most glycosphingolipids from animal tissues. They were phosphatidylethanolamines one of which had only non-hydroxylated fatty acids and the other hydroxy fatty acids in addition to non-hydroxylated fatty acids, respectively. 2. 2. The distribution of the fatty acids was studied by hydrolysis with snake venom phospholipase A (E.C.3.1.1.4.). Hydroxy fatty acids were located in the β-position of the glycerol moiety, differing from the results for Brucella abortus phospholipids in which location in the α-position has been reported. 3. 3. The main hydroxy fatty acid was purified by preparative gas-liquid chromatography. The structure of the hydroxy fatty acid was analyzed by oxidation with lead tetraacetate, proton magnetic resonance, and mass spectrometry, etc. From these results, it was assumed that the main acid was 2-hydroxy-13-methyltetradecanoic acid. © 1969.