The effect of doping aromatic compounds on the structure and physical properties of lecithin were studied using X-ray diffraction and broad-line1H-NMR methods and by the measurement of phase-transition behaviour using an optical method. To examine morphological change in the liposomal structures of doped egg-yolk lecithin systems, myelin figures were observed using a polarizing microscope. The lecithins used were L-α-dipalmitoylphosphatidylcholine (L-DPPC) and egg-yolk lecithin (egg-PC). Xylene and ephedrine were used as a hydrophobic aromatic dopant and a hydrophilic aromatic dopant, respectively. Xylene molecules were located between two ends of the hydrocarbon chains of lecithin molecules set toe-to-toe in the bilayer structure,i.e., the central part of the bilayer. In contrast, ephedrine molecules with water molecules were located between two polar head groups of the adjacent bilayers,i.e., the outer part of the bilayer. The doping of both aromatic compounds increased the stacking repeat distance of bilayer systems. The increase of the bilayer thickness due to the doping of aromatic compounds altered the thermotropic phase transition behaviour. The first phase transition point observed around 120°C for hydrated egg-PC shifted to a low temperature region, and the growing behaviour of myelin figures observed for these doped lecithin/water systems tended to grow in coiling and twisted structures.