A simple one-step hydrothermal method for large-scale synthesis of ultralong single-crystalline Bi2S3 nanowires was reported, and the nanowires were comprehensively characterized. The diameters of the nanowires are about 60 nm, and their lengths range from tens of microns to several millimeters. The structure of the nanowires was determined to be of the orthorhombic phase, the growth direction was along [001], and the growth mechanism was investigated based on extensive high-resolution transmission electron microscopy observations. Optical absorption experiments revealed that the Bi2S3 nanowires are narrow-band semiconductors with a band gap E-g approximate to 1.33 eV. Electrical transport measurements on individual nanowires gave a resistivity of about 1.2 Omega cm and an emission current of 3.5 mu A at a bias field of 35 V/mu m. This current corresponds to a current density of about 10(5) A/cm(2), which makes the Bi2S3 nanowire a potential candidate for applications in field-emission electronic devices.