Supercritical dyeing proceeds in a sequence of multiple phenomena such as dissolution, adsorption, and diffusion involving different timescales. The aim of this work is to highlight the significant role of the dissolution rates of dyes into the supercritical solution. For this purpose, the dissolution rates of different-sized dyestuffs in the supercritical solutions were measured with a newly proposed methodology utilizing in-situ UV/Vis absorption. It was found that the dissolution rate of disperse dyes is enhanced by micronizing the particles with the rapid expansion of supercritical solution process. The dye uptakes of micronized particles in polyester fiber were increased compared to that of the raw particles. This correlation underscores the sensitivity of the final product quality towards the instantaneous dye concentration surrounding the fibers. (C) 2019 Elsevier B.V. All rights reserved.