In this research, an attempt has been made to study the effect of alkali treatment on the dyeing ability of the commercially available modified polyester fabric. The modified polyester was treated with different concentrations of alkali namely 5, 10, and 15%. The treated polyester fabrics were evaluated for the colour strength (K/S) value and comfort properties. The result indicates that the alkali treatment improved the colour strength value considerably for reactive dyes. In the case of natural dye, the colour strength value significantly reduces after subsequent alkali treatment. It is also evident that the alkali treatment considerably reduced the fabric tensile strength. But it has less influence on the tearing strength of the fabric and wickability. However, the alkali treatment increased the water absorbency, water vapour permeability, and air permeability values than the normal modified fabric significantly. Hence, this study suggests that alkali treatment of the modified polyester considerably improves the comfort properties and dye uptake of the alkali-treated fabric, except for the strength factor. Still, further studies need to be done for the optimization of the alkali concentration to restrict the strength reduction in fabric.