Filled skutterudite NaFe4P12 straight single-crystal nanowires 20-40 nm in diameter and 500-800 nm in length were synthesized by a hydrothermal method at 160degreesC for 24 h. The microstructure of the nanowires is investigated by X-ray diffraction, transmission electron microscope and high-resolution transmission electron microscope. The nanowire is a core-sheath structure. The crystal growth of the nanowire occurs along the [0 $(1) over bar $ 1] direction. A vapor-liquid-solution growth mechanism is suggested. (C) 2002 Elsevier Science B.V. All rights reserved.