The present study aims to evaluate the application of coumarin as a green carrier alternative for dyeing of polyester fabrics, as well as to optimize key dyeing parameters in order to obtain greater color strength (K/S) at lower temperatures than 130°C using single azo class dispersed dye. For this purpose, a full-factorial design was used to study the influence of the single and interactive effects of four factors involved in the dyeing process, namely, pH, temperature, and coumarin and dye concentrations. The chosen technique was a 24-factorial, one-center point, and three replicates at the center point resulting on a response surface, which has shown an increase of the color strength of five times at 90°C, and of three times at 100°C when compared to dyeing at the same temperatures without the use of a carrier. In addition, excellent fastness to washing and to rubbing were obtained.