The mechanical properties of ultrahigh molecular weight polypropylene films with various draw ratios have been studied bv WAXD and dynamic mechanical measurements．The“apparent”crystalline modulus(Eappc) evaluated by the X-ray di-ffraction method are about 34—38 GPa for the various samples．The Young’s mod-ulus of the samples is found to become larger gradually and to correlate with the increase in the noncrystalline orientation．For the sample with draw ratio of 69，the Young’s modulus at room temperature is about 27 GPa

which corresponds to about three fourths of the apparent crystalline modulus，and the temperature depe-ndence of the modulus is very small in the temperature region of 一150 to 160℃ These results indicate that the mechanical property and the thermal stability of su-perdrawn films are remarkably improved．Based on the parallel-series mechanical model

the fully straight crystalline fraction and the “true” crystalline modulus EtruG are evaluated and the estimated EtruG is about 47 GPa．