Objective: To study the structure property of a superfine melt blow(MF) non woven material for making medical masks and its filtering functions. Methods: Five kinds of masks were tested and they were: 20 layer gauze mask, cotton spunlace mask, MF outpatient mask, MF medical protective mask Ⅰ and MF medical protective mask Ⅱ. Scanning electron microscope was used to observe the structure of the filtering materials. The aperture of the materials was measured and the filtering efficacy was tested. Results: The diameter of MF fibers was less than 3 ?m and the material made from it was randomly distributed with multi curve channels and complex structure. The filtering efficacy of the new material was 96.2% 99.5% for ambient aerosol particles with a diameter of 0.3 ?m, while the efficacy of 20 layer gauze mask was 50.9%. As for respiratory resistance the former was 26 43 Pa and the later was 48 Pa. Besides, MF mask had good humid proof function and the character of electronic charge, and the later could help capture the particles. Conclusion: The new masks made from MF material has good filtering function and low respiratory resistance, which can be used to prevent SARS virus.