Thermal degradations of 4,4'-diphenylmethane diisocyanate-based thermoplastic polyurethane elastomers were conducted and investigated as functions of heating conditions by using thermogravimetric analysis, ultraviolet-visible (UV-vis) spectroscopy, gel permeation chromatography (GPC), and Fourier transform infrared (FTIR) spectroscopy. The extent of degradation increased with increasing temperatures and times. The degradation was accompanied by crosslinking and was more significant under air than under nitrogen, indicating that a free-radical mechanism was involved. The degradation mainly was due to unstable hard segments and gave a red shift in the UV-vis spectra. The degradation, leading to considerable discoloration, was demonstrated by UV-vis spectroscopy, starting from 240 degrees C in air for 10 min. Heated in nitrogen for the same period of time, the samples did not show considerable discoloration until 280 degrees C. The UV-vis data suggested that the degradation occurred through cleavages of N-H bonds and C-H bonds on the hard segments. Chain scission of polymer main chains, as demonstrated by GPC data, occurred at a temperature as low as 200 degrees C in nitrogen, although cleavage of N-H bonds was not detectable by UV-vis and FTIR spectroscopy at these conditions. FTIR spectroscopy also provided evidence of cleavage of N-H bonds and depolymerization of urethane linkages. Irganox 1010 was found to be an efficient-antioxidant.