In recent years, environmental authorities in Sweden are reporting about high content of antimony in waste water that is discharging from polyester textile dyeing industries. It is known from available scientific publications that, antimony and its compound is harmful for both human and environment. While dyeing of polyester textiles have a commercial importance and in regards to the environmental issues, the industries are looking for the factors those results in high concentrations of antimony in their dyeing waste water. Dyeing of polyester textile requires high-temperature application in association with dyes and process aid chemicals. The waste water that is being produced after dyeing contains a complex mixture of chemicals, where antimony is one of that mixture. To comply with the industries interest, this master thesis work involved the exhaust dyeing of polyester fabrics/yarns and analyzing the dyeing waste water, to determine the amount of antimony diffusion. According to literature studies, the antimony compounds are widely used as catalyst for polyethylene terepthalate (PET) polymerization and hence antimony is present in polyester textiles. The entire experimental work intended to understand the variation of antimony concentration and the factors that are causing high antimony diffusion from polyester textiles during dyeing. The materials which are polyester yarn and fabrics were collected from 3 different dyeing industries of Sweden and the materials were in 9 different types. From material analysis (before dyeing) it has been found there were variations in antimony concentration among the materials. The process parameters that have varied during exhaust dyeing were dyeing temperature, cycle time and process aid chemical (leveling agent) adding options. With the variation in process parameters, the dyeing has performed and the dyeing waste waters have analyzed through inductively coupled plasma sector field mass spectroscopy (ICP-SFMS). The expectations from the experiments were, under specific dyeing process and with same antimony concentration, the materials varying in filament/fiber diameter; big diameter filament/fiber will diffuse less antimony compared to the small diameter filaments. Also, process-wise the antimony diffusion ratio among the materials will accordingly follow the Fick’s diffusion model. To face the environmental issues with sustainability, entire thesis work could provide concentrated knowledge’s with literature evidence for the dyeing industries. As literature study indicates, the dyeing temperature, temperature ramp set and cycle time play major factor while comparing for the expected diffusion ratio. As a gentle process parameter, comparatively lower temperature and cycle time results lower antimony diffusion. The use of levelling agent could be reduced to a level with the appropriateness while added for dyeing. Also, a strong follow-up is needed in the supply chain, for lowering the initial antimony content in the materials. Overall, the findings of this thesis work also keep an importance to do further research on the polyester textile, as during the experiments most of the materials haven’t reacted accordingly as they were expected to react with the Fick’s diffusion model.