The annealing effects on X-ray luminescence of zinc oxide powders have been investigated. Annealing was performed in vacuum and atmosphere. Thereafter, the samples were annealed in Ar : H2 gas mixture. The luminescence bands located at 515 nm after vacuum annealing and at 525 nm after air annealing were detected in the samples. Annealing in hydrogenous ambience had no effect on samples annealed previously in the vacuum. Luminescence intensity of air-annealed powders decreased significantly after annealing in hydrogenous ambience. All samples had complex decay time curves with three exponential constants.