Abstract A series of high temperature stretching experiments has been applied to well characterized commercial PAN-based carbon fiber tows, to determine the combined effects of stretching stress, temperature and dwell time on Young's modulus and tensile strength. The fiber tows were stretched at temperatures of 2600°C and 2800CC for up to 30 minutes, using stresses in the range 25.5 to 127.5 MPa. Although the mechanical properties were found to depend on all three process parameters, similar moduli and strengths were achieved with different combinations of processing parameters. The crucial factor determining mechanical performance seemed to be the overall extension or strain induced during the hot stretching. Although substantial increases in modulus were recorded for all the high temperature treatments, small strains were found to lead to a loss in strength, as previously documented. On the other hand, the strength was improved when higher strains were induced, indicating that fiber strength, the tradit...