Abstract：Certified reference materials for particle number concentration were developed with particle size nominal values of 5, 10 and 25 μm.The certified reference materials candidates were commercial crosslinked polystyrene particle samples, which were sieved again for obtaining narrow distribution samples and their stability were tested. The mean particle sizes of the certified reference materials were obtained by using a high accurate method which can traceable to national length standard.The particle number concentrations of certified reference materials were measured by optical microscope method, and the uncertainty of this measurement process was analyzed and calculated.The results show that the developed certified reference materials satisfy the technical demands of national certified reference materials, which have successfully declared national certified reference materials.

Keywords：particle number concentration; particle counting; certified reference material; polystyrene