Dust removal at high temperature is a vital technology for advanced coal utilizing technologies. Particle size distribution measurements are very important for evaluation of the performance of the dust removal equipment. The cascade impactor like Andersen stack sampler (A.S.S.) is now widely used for the measurement of dust. Particulate matters, such as fly ash, become melting particles at high temperature. It, however, is impossible to apply A.S.S. to melting particles. The authors have developed a particle size distribution measurement method by use of classification during particle sampling, which is available for melting particles. The method is applied to the dust emitted from pulverized coal combustion, and the result is compared with a conventional method. The advanced coal utilizing technologies involve lots of coal treating processes, such as pressurized combustion, gasification, etc., which emit many kinds of dusts. It, therefore, is very important to improve the new method to accurately measure wide size distribution. The optimization of operating conditions of the new method is one of the measures of the improvement. The influence of operating conditions of the method on the measurement accuracy is also investigated. The method has a sufficient accuracy for dust with wide size distribution. (C) 2007 Elsevier B.V. All rights reserved.