Aromatic polyester (PEA) and copolyesters having pendant carboxyl. groups are directly synthesized from isophthaloyl chloride, diphenolic acid and diols by aqueous/organic two-phase interfacial polycondensation, using phase transfer catalysts. The yield and molecular weight of the polyester were remarkably affected by the structure of quaternary ammonium salts and crown ether catalysts. The phase transfer reaction steps are suggested to explain this phenomena. The properties of copolyesters were dependent on the original structure of diols.