Polyacrylonitrile (PAN)/zinc oxide (ZnO) nanocomposites were prepared by solution mixing in dimethylacetamide, followed by film casting, and their physical properties were investigated. The heating scan of differential scanning calorimetry displayed only a single crystallization peak (T-c) without a melting peak, regardless of the presence of ZnO. The incorporation of ZnO nanoparticles decreased T-c by 13 degrees C, and increased the heat of crystallization by 18%. Further, it greatly improved the thermal stability of PAN, even at the ZnO content as low as 0.1 wt %. The nanocomposites showed the UV transmittance peak at 365 nm, whose intensity was increased as ZnO content was increased. The presence of ZnO did not produce new peak nor shift the peaks with respect to PAN in wide angle X-ray diffraction pattern. Introduction of a small amount of ZnO nanoparticles did not have notable effect on the tensile properties. However, 5 wt % loading of the nanoparticles increased the tensile modulus of PAN by 14.5% and decreased elongation at break dramatically. PAN nanocomposites with 5 wt % ZnO did not show any plateau region in stress-strain curve. (c) 2005 Wiley Periodicals, Inc.