Eutectic Bi-43Sn (in weight percent) nanowires with diameters of 20 nm, 70 nm and 220 nm respectively, were fabricated by a vacuum hydraulic pressure injection process using anodic aluminum oxide (AAO) as templates. Novel eutectic microstructure was found within the fabricated nanowires, which 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 that the as the wire diameter reduced, longer Bi and Sn segments formed. In addition, the alternative segmental compositions showed that the ratio of tin to bismuth is approximately 3.3:1. For this process, nanowires were formed from non-ion deposition with liquid alloy; in this way, the composition of nanowires can be controlled precisely in stoichiometry. The size effects on solidification and the formation mechanism of the segmented eutectic Bi-43Sn nanowires have also been investigated during the in situ reheating processes. A directional solidification along the wire axis limits the segmented eutectic nanowire to arrange axially due to directional solidification and the sequential enrichment of two elements. In 70 nm nanowires, the small size confines the convection in liquid, which results in differences in the microstructure and composition profiles between 70 and 200 nm nanowires during the reheating process. In the vacuum hydraulic pressure injection process, the directional cooling helps the formation of single crystal, and the isotropic solidification leads to polycrystalline microstructure. Finally, bismuth oxide-tin oxide (BiOx-SnOx) heterostructure nanowires with a diameter of 70 nm were fabricated by directly annealing Bi-Sn eutectic nanowires. After removal of AAO template with etching solution, a spontaneous oxide was formed on the nanowires, enclosing the Bi-Sn eutectic alloys. While these nanowires went through the annealing process at a heating rate of 50 ℃/ min, the well-annealed oxide nanowires remained solid, straight and segmental. The results of cathodoluminescence (CL) spectrum and photoresponse proved that the products comprised bismuth oxide and tin oxide. This fabrication methodology is a simple way to fabricate one-dimensional oxide nanomaterials. Keywords: Bi-Sn eutectic nanowires, Solidification, Size Effect, BiOx-SnOx nanowires