The thermo-mechanical testing of high performance polyimide films Type HPPST supplied by Dupont® was conducted at different strain rates and in different temperature environments. The stress-strain behavior of materials was investigated, and the dependence of Young's modulus on temperature and strain rate is reported. In view of the uncertainty of the Young's modulus determination, the specimens were tested with unloading-reloading to verify the test results. Constant strain rate uniaxial tensile tests and long-time creep tests at various temperatures were performed to characterize the time-temperature-dependent mechanical property precisely. Cyclic loading tests were also implemented on specimens to investigate cyclic stress-strain behaviors. This research is expected to enhance finite-element-modeling accuracy and characterize material properties precisely. © 2004, Taylor & Francis Group, LLC.