A face mask structure has an upper mask portion, a middle mask portion, and a lower mask portion, which are formed integrally. The upper mask portion has an upper metal stripe disposed at a proper position thereof. The lower mask portion has a lower metal stripe disposed at a proper position thereof. The upper and lower mask portions are folded in opposite directions. When in use, the upper and lower mask portions are spread out to support the middle mask portion. In this way, the face mask structure becomes fitting in with the shapes of human faces. Furthermore, the middle mask portion has multiple folding portions. When in use, the folding portions are stretched out to increase filtering area. Thereby, the inner space of the face mask structure is increased, the air-invasion rate is reduced, and the filtering efficiency is thus improved.