Water dispersible anionic copolyester, obtained from two dimethylester components, dimethyl isophthalate(DMD and 5-sodium such dimethyl isophthalate(DMS) and two biol components, ethylene glycol(EG) and diethylene glycol(DEG) has been synthesized and its chuacteristics as a warp sizer for polyester fabrie has been investigated. Although dispersion of copolyester in water shows lower viscosity, higher adhesive force is recognized when compared with those of aqueous solutions of commercial acrylic sizers. Increase in mole of DMS in dimethyl ester component and DEG in biol component results in the decrease of panicle size of the copolyester dispersed in water and increase of dispersion stability. And the dependence of dispersion stability on the DMS and DEG was discussed in terms of electrostatic and steric stabilization effect in connection with morphological change of particle. And also the effect of DEG content on the glass transition temperature of the copolyester and the plasticizing effect of oil which is an important factor determining the quality of the sizing process was investigated.