Anionic water dispersible copolyesters were synthesized by the polycondensation of dimethyl isophathalate (DUI)/5-sodium sulfo dimethyl isophathalate(DMS) with ethylene glycol(EG)/diethylene glycol(DEG) Molecular structure of copolyester was analyzed by means of NMR, IR and WAXD. Relation between monomer field ratio and copolymer composition was confirmed by NMR analysis and copolyesters were found to have more DEG than those expected from the fled ratio. From the solubility test, the optimum DUS content for water dispersible copolyesters was found to he 10 mol% in dimethyl esters. Water resistance of copolyesters decreased with the increase of DUS or DEG content.