A systematic investigation of the role of hydrogen in hydrogenated amorphous substo-ichiometric silicon oxide films (a-SiOx :H) implanted with erbium is presented. Theexperimental results show that Er3+ luminescence increases with annealing tempera-ture up to 535℃ and then drop sharply. Our work suggests that hydrogen evolutionduring annealing below 535℃ results in a reduction of defects in the films, and hencean improved Er3+ emission.