Abstract: Based on a survey of the mechanism for reactive dyes containing β-hy-droxy-ethyl sulfonyl sulfuric ester on the cellulosic fibre, and the structures of non-ionic nature of disperse dyes, a new range of reactive disperse dyes for polyester cotton blends is proposed. The reaction mechanism for such reactive dyes studied on cellulose is represented by the following equations: If dyeing is carried out by the thermosol process, the following reaction would be expected to take place: It would likely happen that the species D-SO2CH=CH2 being formed could react with cellulosic fibre as in (B) and physically retain within the polyester fibre. A range of azo dyes has been synthesized and is represented with the following general formula:where X and Y are non-ionic groups and could be the same or different, as-C2H5, -C2H4CN, -CH2C6H5, -C2H4OCOCH3, -C2H4COOCH3, etc., A is H, R(Alkyl),-NHCOR, etc. and B is H, halogens, -OR. etc. No ionic groups are present in the dye molecule. The β-hydroxy-ethyl sulfonyl sulfuric ester group serves both as reacting group and solubilizing group which renders the dyes to be water soluble. These dyes are found to be suitable for dyeing and printing on the polyester-cotton blend fabrics in the presence of weak alkali by the thermosol process between 190-210℃ for 1.5-2min. The formation of covalent bond between the dye and cellulosic fibre is proved by unique extraction method. The detention of vinyl sulfone dye formed in the polyester portion of polyester-cotton blends is evidenced by chromatography, IR spectroscopy and NMR identifications.