The transesterification of dimethyl terephthalate(DMT) with 1,3-propane diol(PDO) was invesigated in the presence of catalyst, titanium (IV) butoxide, at 175∼190℃. The degree of esterification reaction was measured by the output of methanol which was distilled from the reactor. The polycondensation of PTT was also investigated by the required current that mixing speed was kept constant, in the presence of titanium(IV) butoxide and thermal stabilizer at 260∼280℃.