Polyester (PET) is semi-crystalline thermoplastic fibre used in many fields. By nature, polyester fiber is hydrophobic owing to the lack of any hydrophilic groups in its structure. Therefore, it is necessary to impart desired properties by introducing specific functional groups on the surface of the fiber to make it more practically useful. Alkali and amine treatment with caustic soda and ethylene diamine, respectively were studied in the present work for surface modification. Dyeing of the treated samples with anionic dyes such as reactive dye, acid dye and vat dye as well as disperse dye for a comparison purpose was also studied. Aminolysis reaction of Poly (ethylene terephthalate) (PET) fibers with ethylene diamine gives amino (~NH2) functional groups whereas hydrolysis by sodium hydroxide gives hydroxide (~OH) functional groups on the surface of the polyester fabric as observed by the Fourier Transform Infrared Spectroscopy(FTIR). The effects of temperature, reaction time, ethylene diamine and caustic soda concentration were studied in order to find out the conditions in which best results dyeing could be obtained. The dyeability of treated samples at boil with reactive, acid and vat dye was observed to increase with temperature, reaction time, and reagents concentration at optimum conditions due to significant increase in number of reactive functional groups on the surface of the fiber and considerable decrease in glass transition temperature, Tg which was indicated by Differential Scanning Calorimetry (DSC). The colour strength (K/S) values of all anionic and disperse dyed samples were measured using spectrophotometer and compared with the control samples. There is also a significant improvement in fabric water wettability, hand and comfort ability with good fastness properties (wash, rubbing and light) due to these surface modifications although there is loss in weight and tensile strength because of chain scission, as the reaction proceeds.