A visible-light-promoted hydroxylation of quinoxalin-2(1H)-ones using recyclable graphitic carbon nitride (g-C3N4) as a heterogeneous photocatalyst has been developed. This protocol enables the selective synthesis of various hydroxyl-containing quinoxalin-2(1H)-ones in good to excellent yields under an ambient air atmosphere. Importantly, this heterogeneous catalyst can be used at least six times without significant loss of activity.