A series of nanocomposites of poly(ethylene terephthalate) (PET) with the organoclay dodecyltriphenylphosphonium-mica (C,,PPh-mica) were synthesized with the in situ polymerization method. PET hybrid fibers with various organoclay concentrations were melt-spun at various draw ratios (DRs) to produce monofilaments. The thermomechanical properties and morphologies of the PET hybrid fibers were characterized with differential scanning calorimetry, thermogravimetric analysis, wide-angle X-ray diffraction, electron microscopy, and universal tensile analysis. The organoclay was intercalated in the polymer matrix at all magnification levels, and some of the agglomerated organoclay layers were greater than 50 nm thick. The thermal stabilities and initial tensile moduli of the hybrid fibers increased with an increasing clay content for DR = 1. For DR = 1, the ultimate tensile strengths of the PET hybrid fibers increased with the addition of clay up to a critical clay loading and then decreased above that critical concentration. However, the tensile mechanical properties of the hybrid fibers did not improve with increasing DR. (c) 2005 Wiley Periodicals, Inc.