A series of coloured polyesters have been synthesized by interfacial polycondensation reaction of terephthaloyl chloride and various bis-azo dials. The bis-azo dials have been prepared from two different heterocyclic dials, 7,7'-dihydroxy-4,4,4',4'-tetramethyl-2,2'-spirobis [chroman] and 2,9-di(2-dimethyl-p-hydroxy benzyl)-5a,10b-dihydro benzofuro [2,3-b] benzofuran by coupling with various diazotized fast bases. These bis-azo dials (dyes) were characterized by their m.p., % yield, elemental analysis and uv-visible spectroscopy and applied on nylon and polyester fibres and their dying performance were assessed. These dyes showed fair to fairly good fastness to light and very good to excellent fastness to washing, rubbing, perspiration and sublimation. All the coloured polyesters were characterized by their elemental analysis,. ir and uv-visible spectroscopy. Their viscosity, solubility, bleeding test and thermogravimetric analysis were also studied.