Abstract: In order to achieve salt-free dyeing of cotton fabrics with reactive dyes,a water-soluble amino-terminated hyperbranched polymer(HBP-NH2) was synthesized from methyl acrylate and diethylene triamine by melt polycondensation.Cotton samples were pretreated with the aqueous solution of HBP-NH2(6 g/L) in the presence of citric acid(2 g/L) and sodium hypophosphite(3 g/L) and then dyed with reactive dyes.Results demonstrated that the pretreated cotton samples displayed markedly enhanced colour strength,and the washing fastness,rubbing fastness and levelling properties were satisfactory.It suggested that HBP-NH2can be applied in reactive dyeing of cotton fabrics as a salt-free auxiliary for various reactive dyes.