Abstract: The optical phase conjugation and photoisomerization of some films of two kinds of polyesters functionalizied by 4-bis(N,N hydroxyethylene)-imino-4-nitroazobenzene have been studied.The photoresponsive mechanism of these films was explained quite well by a model of four-level energy system,which was consisting of two pairs of siglet states of trans and cis isomers,respectively.Photoismerization was the main intramolecular relaxtion between both two-level energy systems.Investigation on effects of pump intensities,polyester structures and thicknees of films has been also carried out.