Modified polyethylene terephtalate(M-PET) was obtained by copolymerizing dimethyl terephthalate(DMT), ethylene glycol, and dimethyl 5-sulfoisophthalate(DMS) and antistatic polyester material has been prepared by exposing M-PET containg ferric chloride to pyrrote vapor. The DMS component in M-PET was confirmed by the analysis of IR and NMR spectra. The formation of polypyrrole(PPy) in M-PET matrix was also confirmed by the analysis of IR spectrum. The changes of physical structure due to the insertion of ferric chloride and formation of PPy in M-PET have been investigated by analysing wide-angle X-ray diffraction curves. The surface of the antistatic polyester film showed the continuous phase of granular PPy, which was formed through the film thickness. The physical properties of antistatic polyester was satisfiable, that was, the tensile strength and the elongation at break retained 80 and 90% of those of M-PET matrix, respectively. But the modulus retained about 60% of M-PET matrix.