A manufacturing method for a metallic housing of an electronic device is provided. The method includes providing a die-casting mold, including a male die and a female die engaging with the male die, the male die defining a pouring gate therein, and the female die defining a cavity therein corresponding to the pouring gate; positioning a metallic outer case in the cavity of the female die as an insert; assembling the male die to the female die to cover the cavity, thereby communicating the pouring gate with the cavity; casting pressured molten metal-alloy into the cavity via the pouring gate to form an inner structural member embedded in an inner side of the outer case; dissembling the male die from the female die to expose the cavity, and removing the outer case and the inner structural member from the female die.