A fixing assembly for a fan module is combined in a housing and includes at least one fixing base and at least one bottom pad. The fixing base has an accommodating space and a plurality of positioning portions in the accommodating space. The positioning portions are provided in pairs and symmetrical to each other. The locations of the positioning portions are designed for positioning various sizes of heat-dissipating fans. The bottom pad is configured to support the bottom of the fixing base. By this structure, various sizes of fan modules can be positioned in the housing.