We report that the resistance of a chemical vapor deposition (CVD) grown graphene film transferred onto an SiO 2 substrate increases to higher saturation values upon exposure to light of decreasing wavelength from the visible to ultraviolet. Light in the visible range causes a slight increase of up to 10% in saturation resistance. A significant increase in resistance is found starting at about 400 nm. The saturation resistance approaches up to 3 times the original resistance at 254 nm after 5 min. When the light is removed, the resistance falls to its original value with a time constant of several days. The effect is not observed for samples of CVD-grown graphene films on SiO 2 that have been heated in vacuum at 600 ℃, nor single-crystal graphene mechanically exfoliated onto SiO 2 . We attribute the effect to photo dissociation of interfacial molecules such as H 2 O adsorbed between the CVD-grown film and SiO 2 substrate at grain boundaries in the film.