Polypropylene (PP)/nanoclay composite filaments were produced by melt spinning and characterized to study the effect of the compatibilizer and the role of the nanoclay in improving the physical properties. The compatibilizer was maleic anhydride grafted PP. Clay loadings up to 1 wt % with up to 3 wt % compatibilizer were explored. There was a significant improvement in the tensile, thermal, and dynamic mechanical properties and creep resistance of PP/nanoclay composite filaments over neat PP filaments at very low clay loadings of 0.25-0.5 wt % and a compatibilizer/clay ratio of 2:1. The properties were correlated to the morphology of the nanocomposite filaments, which was investigated with differential scanning calorimetry, X-ray diffraction, and transmission electron microscopy. (c) 2006 Wiley Periodicals, Inc.