A method of preparing high molecular weight poly(ethylene terephthalate)(PET) was developed. In heat transfer agents, such as biphenyl, terphenyl, benzophenone, diphenyl ether, cyclohexylbenzene, and hydrogenated triphenyl, PET powder was postpolycondensated under preheated nitrogen flow of 31/min. Among the heat transfer agents biphenyl, cyclohexyl benzene, and hydrogenated triphenyl had effects on the increase of molecular weight of the polymer, and PET of intrinsic viscosity(IV) 1.56 or 92,000 could be prepared from the polymer of IV 0.62. The porous fibrillar PET was made by dissolving the polymer in phenol/tetrachloroethane and precipitating the polymer solution in acetone. This porous fibrillar PET was solid state polycondensated under nitrogen flow or in hydrogenated triphenyl as the heat transfer agent, and the polymer was capable of producing much higher molecular weight in comparison with the ordinary melt or solid state polycondensation product even at lower reaction temperature. Finally PET having IV 2.95 (221,000) and carboxyl content of 3.3 eq.110sg PET was produced via two steps postpolycondensation in hydrogenated triphenyl from the porous fibrillar PET (IV 0.62) and its polydispersity index was 2.31.