The effect of diphenyl terephthalate(DBW) on the polycondensation reaction of his(2-hydroxyethyl) terephthalate(BHET) has been investigated using various catalysts. The analysis of byproduct produced from the polycondensation by high performance liquid chromatofyaphy(HPLC) and of the molecular weight of polycondensed poly(ethylene terephthalate) (PET) by gel permeation chromatography showed that the increasing rate of the molecular weight of PET by chain coupling reaction of DPT was enhanced by zinc acetate, while the polydispersity and the increasing rate of the molecular weight were decreased by sodium ethoxide owing to its promoting effect of the ester-ester interchange reaction. Assuming that the chain coupling reaction of DPT with PET chains 1311ows a third order reaction, the kinetic consideration of the polycondensation reaction of BHET was performed using the analysis results of byproduct during the polymerization by HPLC.