The infrared absorption of U-center in KCl and KBr was measured. The ratio of the absorption wavelength of the U-center consisting of a D− ion to that of a H− ion was 1.39 for KCl and 1.41 for KBr. These values were in good coincidence with the ones expected theoretically. The half width of the absorption band of KCl•KD was slightly larger than that of KCl•KH. The effect of the U-light irradiation at high temperature was also investigated. The absorption intensity was decreased by the irradiation, and restored to almost the original intensity after further heat treatment at 200°C.