A microwave oven includes an outer housing defining an accommodating chamber therein and having a first cooling air inlet and a first cooling air outlet therein; an inner housing disposed within the accommodating chamber and defining a heating chamber therein, the heating chamber having a second cooling air inlet and a second cooling air outlet communicated with the first cooling air outlet, a cooling air passage being defined between an upper surface of the inner housing and a top wall of the accommodating chamber and communicated with the second cooling air inlet; a cooling fan having an air inlet communicated with the first cooling air inlet via an air inlet passage and an air outlet communicated with the cooling air passage; and an electrical component disposed within the cooling air passage.