Single-crystalline nanowires are successfully prepared from a small organic functional molecule, tris(8-hydroxyquinoline)aluminum (Alq3), by an adsorbent-assisted physical-vapor-deposition method. The introduction of adsorbents can decrease the sublimation temperature of Alq3, and slow the weight-loss process markedly, which is proven to be indispensable in improving the uniformity of the as-prepared Alq3 nanowires. Measurements of the optical properties reveal that the absorption spectra of the Alq3 nanowires show an obvious blue-shift with decreasing diameter. The photoluminescence vibrational fine structure emerges and becomes pronounced with increasing excitation energy, which is attributed to the ordered orientation of the Alq3 molecules in the nanowires. Furthermore, the Alq3 nanowires are fabricated into an electroluminescent device, which has an obvious size-dependent performance.