a-Si:H/SiO2 multilayers were layer by layer deposited and in situ plasma oxidized in a plasma-enhanced chemical vapor deposition system. Strong and stable blue photoluminescence at room temperature was observed from the as fabricated a-Si:H/SiO2 multilayers. By controlling the thickness of the a-Si:H sublayer from 4 to 1.5nm,the photoluminescence peak blueshifts from 465 to 435?nm. X-ray photo electron spectroscopy indicates that the oxide layer is of stoichiometric SiO2. Good passivation of a-Si:H/SiO2 interface is testified by C-V. Periodical structure and sharp a-Si:H/SiO2 interface is shown by transmission electron microscope. Combined with the measurements of absorption and photoluminescence, the origin of blue photoluminescence is attributed to the recombination of electrons and holes near the band-tail in a-Si:H sublayer under one-dimensional quantum confinement effect.