Considering the stress concentration and the similarity of stress distribution near the notch root, we have obtained a fatigue failure criterion for notched FRP plates in terms of a combination of the maximum elastic stress, the notch-root radius and the number of loading cycles to fatigue-damage initiation. To evaluate the fatigue damage near the notch root during fatigue test; we measured successively the luminance distributions by means of the luminance measurement technique with a CCD camera. The aims of the present research are to provide experimental evidence of the validity of the fatigue failure criterion as mentioned above and to show that the decrease of luminance is associated with irreversible damage and microfracture, The investigation is accomplished by obtaining experimental data of fatigue tests on the notched plates of a glass fiber-reinforced polycarbonate. To reveal the initiation and growth of microfracture along with the luminance decline, we observed the transverse section of the fatigue-damage zone near the notch root. The experiment shows that numerous microcracks initiated the end corner of a glass fiber and it is likely that several microcracks joined together and grew into a main crack.