High-strength composite fibers were prepared from poly(vinyl alcohol) (PVA) and multiwalled carbon nanotubes (MWNTs) functionalized with PVA matrix. Esterification between MWNTs and PVA was confirmed by Fourier transform infrared, Raman spectroscopy, thermogravimetric analysis, transmission electron microscope, and atomic force microscope. Homogeneous dispersion of PVA-functionalized MWNTs in dimethyl sulfoxide was affirmed by optical micrographs and particle size analysis. The PVA-functionalized MWNTs/PVA (1 wt %) composite fibers prepared by gel spinning and hot-drawing process exhibited tensile strength and modulus as high as 2.1 and 34 GPa, respectively, showing a 75% increase in tensile strength and 35% increase in modulus compared with pure PVA fibers. The mechanical properties were also much higher than untreated MWNTs/PVA (1 wt %) composite fibers and carboxylated MWNTs/PVA (1 wt %) composite fibers. From wide-angle X-ray diffraction, scanning electron microscopy, and Raman spectra analysis, higher mechanical properties of PVA-functionalized MWNTs/PVA composite fibers are attributable to homogeneous dispersion of MWNTs in PVA matrix, stronger interfacial adhesion between MWNTs and PVA matrix, and uniaxial orientation of MWNTs along fiber axis. (C) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 128:1044-1053, 2013