Eutectic Bi-43Sn (in weight percent) nanowires with diameters of 20 nm, 70 nm and 220 nm respectively, were fabricated by a hydraulic pressure injection process using anodic aluminum oxide (AAO) as templates. Novel eutectic microstructure was found within the fabricated nanowires. which are composed of alternating Bi and Sn segments along their wire axes. Within the segments, the electron diffraction analysis revealed single crystalline structures of Bi and Sn elements respectively. Parameters that control the nanowire fabrication process were discussed. It was found out that as the wire diameter reduced, longer Bi and Sn segments formed. (C) 2009 Elsevier B.V. All rights reserved.