Kinetics of the dyeing process of modified polyethylene terephthalate with disperse dye are shown in this paper. The modification of the fibers was performed with an aqueous solution of slaked lime with the simultaneous action of ultrasonic waves. The dyeing of the fibers was performed in a discontinuous-batch process, with a change in the initial dye concentration (20 - 120 mg dm-3) and dyeing time (5 - 60 min). Several kinetic reactions (Pseudo first, Avrami and Modified Freundlich) and diffusion models (Weber&Morris, Boyd, and Film diffusion) were used to test the experimental data from the dyeing process. It has been found that dyeing of modified fibers gives better results than dyeing of unmodified polyester, under the same conditions. With the increase of the initial dye concentration, a degree of exhaustion decreases (76,2 - 57,4 %, for equilibrium time of dyeing) and the absorption of disperse dyes per unit mass of fibers increases (1,5 - 6,9 mg g-1, for equilibrium time of dyeing). During the dyeing process, the initial concentration of the dye decreases, whereas the capacity of the adsorption increases. A linear simulation of the kinetic dyeing parameters showed that the Modified Freundlich reaction model dominated, while of the kinetic diffusion models the Boyd equation was most favorable.