By in siti polyconclensation, a intercalated poly(ethylene terephthalate)/organomontmorillonite nanocomposite was prepared after montmorillonite (MMT) had been treated with a water-soluble polymer. This nanocomposite was produced to fibers through melt spinning. The resulting nanocomposite fibers were characterized by X-ray diffraction (XRD), differential scanning, calorimeter (DSC), and transmission electron microscopy (TEM). The interlayer distance of MMT dispersed in the nanocomposite fibers was further enlarged because of strong shear stress during processing of melt spinning. This was confirmed by XRD test and TEM images. DSC test results Showed that incorporation of MMT accelerated the crvstallization of poly(ethylene terephthalate) (PET), but the crystallinity of the drawn fibers just had a little increasing compared with that of neat PET drawn fibers. Also compared with pure PET drawn fibers, tensile strength at 5% elongation and thermal Stability of the nanocomposite fibers were improved. (C) 2005 Wiley Periodicals, Inc.