The formation of surface relief grating upon light irradiation on a composite film of conducting polymer with rigid main chain structure and acrylate polymer containing azo-substituent with soft main chain structure has been studied. The diffraction efficiency of the photo-induced grating decreases with increasing concentration of conducting polymer with respect to the polyacrylate in the concentration range higher than 3%. This implies that the height of surface relief on the him is lowered upon doping conducting polymer, which is confirmed by an atomic force microscope observation. It has been found, however, that the formation of surface relief grating is promoted by slight doping of conducting polymer (<3%) and progresses even after stopping light irradiation on the composite film. Anomalous angular dependence of photoluminescence from the composite film having relief grating on it has also been found.