Three kinds of techniques have been developed on electrostatic classification of particle size. The first utilizes linear electrostatic traveling field. A particle conveyer consisted of parallel electrodes was constructed and four-phase traveling electrostatic wave was applied to the electrodes to transport particles on the conveyer. Particles were classified with size under the voltage application of appropriate frequency based on the feature that the direction of particle transport was changed depending on the frequency of the traveling wave and the particle diameter. The second technique utilizes a circular electrostatic conveyer similar with the mass spectroscopy. Particles were classified with size because a locus of the particle in centrifugal field depended on the weight of the particle. The third is the combination of the linear conveyer and an electrostatic separation roller located at the end of the conveyer. Small particles were attached onto the roller charged by a charger roller. These techniques have been expected to be utilized to the classification of the particle size and a charge-to-mass ratio of toner and carrier particles used in electrophotography.