Fatigue of Pb(Zr0.52Ti0.48)O3(PZT) thin film capacitors under UV light (He-Cd laser, λ=325 nm) was studied. The remnant polarization of PZT films increased upon UV light illumination. The change in the polarization of PZT films upon UV light illumination increased with fatigue cycling. The photoresponse of PZT films under red light (He-Ne laser, λ=633 nm) was also studied. The difference in the steady-state photocurrents of negatively and positively poled PZT films was observed and was found to increase with fatigue cycling. Those results were examined within the framework of polarization screening by defects which is suggested to be responsible for fatigue of PZT films. This leads to a conclusion that more charged defects responsible for fatigue are involved in the fatigue process through internal polarization screening with fatigue cycling.