For conservation and restoration of cultural property, it is necessary to know the chemical composition of the oject and the quantity of each components. Thermogravimetric analysis - fourier transform infrared spectrophotometric analysis (TGA-FTIR) is an useful analytical technique which can be employed to identify and determine, the chemical composition of materials especially polymeric substances. This paper will discuss the application of TGA-FTIR on the determination of the chemical composition of the lacquer films from Melanorrhoea usitata commercial lacquer and ancient Thai lacquer. Characterization of oriental lacquer by TGA-FTIR also be discussed.