Si quantum dots (QDs) embedded in SiO 2 can be normally prepared by thermal annealing of SiO x (x<2) thin film at 1100°C in an inert gas atmosphere. In this work, the SiO x thin film was firstly subjected to a rapid irradiation of CO 2 laser in a dot by dot scanning mode, a process termed as pre-annealing, and then thermally annealed at 1100°C for 1h as usual. The photoluminescence (PL) intensity of Si QD was found to be enhanced after such pre-annealing treatment. This PL enhancement is not due to the additional thermal budget offered by laser for phase separation, but attributed to the production of extra nucleation sites for Si dots within SiO x by laser irradiation, which facilitates the formation of extra Si QDs during the subsequent thermal annealing.