Studies of thermal decomposition on poly(oxytetramethylene) glycol have been conducted by pyrolysis gas chromatography-mass spectrometry, infrared spectroscopy, and thermogravimetric analysis (TGA). The major volatile decomposition products are suggested to be a series of molecules made up by the repetition of oxytetramethylene with formyl and/or methyl ends. Absorption peaks, associated with formyl appear in infrared spectrum of a sample preheated at 523 degrees K lower than the onset temperature obtained from the TGA curve. The isothermal TGA curves fit well to the Shimha rate equation for the random decomposition of polymers. The proper activation energies obtained from the thermally controlled and the isothermal TGA data are approximately 60-70 kJ mol(-1) and lower than those for other polymers in ordinary thermal decomposition. These data suggest that the major reaction in the thermal decomposition of poly(oxytetramethylene) glycol is an ether cleavage. Two pathways, a radical scission accompanied by beta-hydrogen transfer and a nonradical reaction through a four-membered ring transition state, are proposed and discussed for the ether cleavage.