A heat-dissipating fan fixing device used for accommodating and fixing a fan and mounted on a case is provided, which includes a frame, a plurality of hooks and an elastic buckle piece. The frame has a first end and a second end being opposite to each other. Between the first end and the second end, an accommodating space through the frame is formed for accommodating and fixing the fan. The hooks extend from one side edge of the first end, and the elastic buckle pieces are formed by bending along another side wall of the first end. Thus, when the frame is joined with the case, firstly, each hook catches the case, and then, the elastic buckle piece is embedded into the case, thereby mounting the fixing device with the fan on the case.