We wish to report the method of isolation and chemical characterization of a new lipoamino acid ester from Streptomyces sioyaensis, in which the presence of a lysine-containing lipid was previously reported. The substance, for which we propose the name siolipin A, is a lipoamino acid ester and defined as a fatty polyalcohol ester of Nε-acyl lysine (I). The wet mycelium of this microorganism was washed with acetone. The dried mycelium was extracted with chloroform-methanol (2 : 1, by vol.) to give a lipid extract (100 to 200 mg per g cell, yield depending on culture conditions such as pH and growth age). The extract was fractionated by chromatography on silicic acid to give a cephalin fraction (about 1.8% of total lipid recovered) containing phosphatidylethanolamine and siolipin A, which could also be obtained by elution of the extracts with chloroform-methanol (7 : 3, by vol.) on DEAE-cellulose column chromatography, showing siolipin A is neutral. To separate siolipin A from phosphatidylethanolamine, the cephalin fraction (493.5 mg) was hydrolyzed by snake venom (Habu, Trimeresurus flavoviridis, Hallowell) phospholipase A (degrading phosphatidylethanolamine to lyso-form while siolipin A remained intact), and reaction products were separated by silicic acid chromatography. Purified siolipin A was recrystallized from methanol to a white amorphous powder (about 0.1% of total lipid), with mp. 132-134°C after previous sintering, ninhydrin positive, containing neither glycerol nor phosphorus. Paper chromatography of 6 M HCl hydrolysate (24 h) showed lysine and fatty materials (fatty acids and fatty alcohols); amino acid autoanalyzer (Hitachi KLA-2) revealed 1 mole lysine per mole siolipin A (molecular weight 630 by vapour pressure method, 1.36 μmoles lysine in 1 mg siolipin A). Dinitrophenylation followed by 6 M HCl hydrolysis (105°C, 24 h) gave Nε-DNP-lysine (identified by paper electrophoresis and chromatography), indicating Nε-protected lysine derivative. Infrared spectrum showed primary amine (3426 and 1596 cm⁻¹), hydrocarbon chain (2930, 2870, 1470, 1386 and 725 cm⁻¹), ester function (1734, 1265 and 1250 cm⁻¹), and amide group (1643 cm⁻¹); [α]ᴅ +5.7±0.3 (c, 1.150 in chloroform). Elemental analysis found C 67.64, H 11.47, N 4.09, matching calculated values for C₃₇H₇₀N₂O₇ (C 67.66, H 11.57, N 4.15%). Mild alkaline hydrolysis of siolipin A (10.3 mg) cleaved ester linkage; silicic acid chromatography of products gave fatty alcohol (1.7 mg, MW ~240, less volatile fatty polyalcohol, structural studies ongoing) and lysine-containing lipid (IIa, 0.9 mg, mp. 162-163.5°C after sintering, MW 434, infrared showed no ester linkage but primary amine, hydrocarbon chain, amide group; esterification with diazomethane gave IIb with RF similar to siolipin A on thin-layer chromatography). Hydrolysis of IIa (2 M HCl, 18 h) gave lysine (identified by autoanalyzer and gas-liquid chromatography) and fatty acids (R₁COOH) which were normal and monohydroxy in 1:4 ratio (thin-layer chromatography), with non-hydroxylated (n-16, n-17, n-18, n-19) and unidentified hydroxylated fatty acids (gas-liquid chromatography). Synthetic Nε-palmitoyllysine (IIc, from Nε-carbobenzyloxy-L-lysine acylated with palmitoyl chloride and deprotected) had identical infrared spectrum and thin-layer chromatography with natural IIa. Based on these results, structure I was proposed for siolipin A. Moreover, an ornithine-containing lipid (siolipin B) was found in the same organism: early culture mycelium contains only siolipin A, while stationary phase mycelium contains much siolipin B, which may be related to ornithine-containing lipids in Mycobacterium, Rhodopseudomonas spheroides and Rhodospirillum rubrum.