A study on LiNbO3 crystal irradiation by pulsed KrF excimer laser beam is presented. The interaction with the 248 nm laser light modifies the material properties so that, when the irradiation is switched off, a time-periodic variation in the material reflectivity, depending on the irradiation conditions, was observed. This phenomenon can be explained in terms of the electro-optic effect induced by the buildup of internal electric fields since the compositional characterization, performed by the secondary ion mass spectrometry, showed no modification in the element concentration and the high resolution x-ray diffraction did not detect any structural deformation within the crystal.