The Synthesis of long chain fatty acid containing azobenzene and (Cn-Azo) was optimized, starting from p-(p'-hydroxy phenyl azo)-benzoic acid and the product of reaction containing azobenzene chromophores was investigated by ultraviolet spectrophotometery in chloroform solvent at the various temperature. In addition, Reversibility and stability of azo compounds have been measured by means of Ultraviolet and the structure of these compound were ascertained by means of FT-IR and NMR. Recrystallization of reaction product in the solvent results the experimental yield obtained about 62.93% p-(p'-octadecyloxy phenyl azo)-benzoic acid. Long chain azobenzene derivatives in chloroform solution are induced photoisomerization by u. v. and visible light irradiation. The solution of long chain fatty acids(Cn-Azo) containing azobenzene are possible of being applied to functional molecular devices such as photomemory and light switching.