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Quantum dot (QD) emits light of characteristic wavelength which depends on the size of the QD particles, and thus the quality control of QD requires accurate determination of its size distribution. Field-flow fractionation (FFF) is a separation technique that is well suited for the characterization of colloidal particles. In this study, CdS-QD particles were synthesized by a simple one-step γ-ray irradiation. Then asymmetrical flow FFF (AsFlFFF) and sedimentation FFF (SdFFF) were tested as tools for characterization of the particles. The single crystallite size of CdS-QD was measured to be about 4 nm by X-ray diffraction (XRD), UV-VIS absorption spectroscopy, and transmission electron microscopy (TEM). TEM images indicate that the particles were agglomerated to form larger secondary particles (∼ 110 nm). Effects of the various experimental parameters of FFF including the type of dispersing agent, the ionic strength of the carrier liquid, and strength of external field were investigated. It was found that, among the dispersing agents tested, a mixture of anionic and nonionic surfactants tends to give better elution of CdS particles than anionic or nonionic surfactants. Results suggest that FFF can provide some advantages over dynamic light scattering (DLS) or TEM for size characterization of CdS particles, and with a proper optimization, FFF (AsFlFFF or SdFFF) could become a useful tool for stability study as well as size analysis of nanoparticles such as the CdS particles synthesized in this study. [ABSTRACT FROM AUTHOR]