The ethylene glycol dibenzoate(EDB) was used as the model compound of PET. The thermal degradation behavior of EDB was studied at 28O˚C by adding the titanium tetrabutoxide as a catalyst and hindered phenol and phosphate type as a stabilizer. The estimation of stabilizers with GC and colorimeter using EDB as model compound was suitable for the estimation of PET stabilizers. The color seems come from the polyenes produced by the degradation from polyvinyl benzoate rather than from the condensation of acetaldehyde. From the pyrolysis product of EDB, acid value was measured by using the GC. The low acid value is observed as the lower amount of Irganox 1222 and the higher amount of TMP and TEP is used. Acid value is not agreeable with color difference. The hindered phenol type was good in the view of acid value and phosphate type was good in the view of color difference. The use of hindered phenol and phospate mixture do not give obvious synergistic effect. Excellent retardation of coloring is appeared as the used amount of hindered phenol type is small and phosphate is large. In the case of phosphate, excellent retardation of coloring is appeared as the carbon number of substitute is small.