The control of luminescense intensity from rare earth ion (En(3+), Ta3+)-doped polyimide (PI) nanoparticle film by UV-irradiation and thermal treatment is reported. In the system, it was observed that luminescence intensity assigned to rare earth ion. increased with increase of UV-irradiation time, whereas the intensity decreased with elevation, of thermal treatment temperature. It was estimated that the mechanism of the above phenomena is based on a reversible change in an energy transfer probability from PI to rare earth ion by the UV-irradiation, and the thermal treatment.