Abstract: The particle size is a very important characteristic index for geological powder reference materials. For a long time, the particle size of geological reference materials had been determined by sieving analysis or settlement separation, and expressed in percentage of that part which passes through a certain mesh screen (normally -200 mesh). In recent years, laser particle size analyzer, reflecting the modern techniques for particle size determination, had been introduced into the preparation of ultrafine size reference materials. In turn, the expression model of particle size was substituted by the intuitive particle size distribution plot and specific particle sizes. The introduction of this technique markedly improved the determination and expression levels of particle size of geological powder reference materials. In this paper, the particle size distribution was determined by laser particle size analysis technique for typical geological reference materials that had been widely used. The purpose of this study is to provide a rational and practicable basis for the usage of those reference materials and their uncertainty evaluation. In addition, some suggestions were also presented for the further study on the determination and expression of particle size for geological reference materials and other geological analysis samples.