The self-excited oscillation of neck propagation during cold drawing of polymer films has been examined experimentally. On the basis of Barenblatt's model considering a thermo-mechanical coupling at the neck, the temperature rise at the neck has been studied with an infrared camera. The temperature began to rise in a range showing a negative velocity dependence of the applied load. The behavior is consistent with the view of thermo-mechanical coupling. The temperature rise was up to 80 degreesC (>T-g) and explains the occurrence of crystallization for faster drawing rates. It has also been confirmed that the temperature rise follows the oscillation of stress due to the coupling.