In spite of the usefulness of phospholipid vesicle, there are limitations of its appication to drug delivery system due to its low stability. Fatty acids are widely distributed in an living organisms as a constituent of various complex lipids. There is the effect of size reduction by addition of fatty acids to vesicle as other nonionic amphiphiles, its degree is varied with the mole fraction and the acyl chain length of fatty acid. The effective size of headgroup is reduced because of hydrogen-bonding interaction between phospholipid and fatty acid, and vesicle will be smaller hydration shell, this leads to size reduction. Fully protonated fatty acids are only very weakly hydrophilic and thus it offers dilution tolerance to vesicle. In proportion to reducing of chain length of fatty acid, the morphology of vesicle shifts highly to the low dimension microstructure(i.e. vesicle to bilayer and/or cylindrical structure). In the present work, I studied the potential of phospholipid/fatty acid mixture for transdermal drug delivery system.