A novel soluble azo polyimide has been prepared from a post azo-coupling reaction scheme．The polyimide-based precursor polymer was obtained from the polycondensation of N

N-bis [(3

4-dicarboxypbeny anhydride)-l-carboxyethyl]aniline and 4

4′-diamino-4″-bexadecyloxtriphenylmethane．It is soluble in polar organic solvents such as tetrahydrofuran(THF) and N

N-dimethylacetamide (DMAc)．The azo polymer was synthesized by the reaction of the polyimide-based precursor polymer and diazonium salt．Both the precursor polymer and the azo polymer were characterized by 1H-NMR

DSC

FTIR and UV-Vis spectrometry．The effect of long alkyl side-chain on the enhancement of solubility was confirmed．When the spin-coated azo polymer film was exposed to an interference pattern of Ar+ laser

regularly spaced sinusoidal surface relief grating (SRG) was formed with depths up to 200 nm.The diffraction efficiency of the detecting laser was recorded to monitor the forming process of SRG and the surface structure on the film was also observed directly by using an atomic force microscope. The result shows that the soluble azo polyimide with surface-relief-grating-forming ability has been successfully synthesized．