A heat-dissipating module includes a first fan unit and a second fan unit, which are serially connected together to provide an air inlet and an air outlet. Each of the first fan unit and the second fan unit includes a casing and an impeller. At least one side air inlet is defined in at least one of a plurality of sides of the casing of the first fan unit and a plurality of sides of the casing of the second fan unit. The air inlet amount and the air outlet amount of the second fan unit are increased by the side air inlet. The air density distribution is uniform, and the wind noise during operation is lowered.