Gallium phosphide (GaP) nanowires of 22 nm in diameter and hundreds micrometers in length were synthesized by laser ablation of a powder mixture of GaP and gallium oxide (Ga2O3). The morphology and microstructure of GaP nanowires were investigated by transmission electron microscopy. Twins and stacking faults were observed on {111} planes of the GaP nanowires with special morphologies, and the formation of these defects was discussed. The growth of the GaP nanowires can be described by an oxide-assisted mechanism involving several oxidation-reduction reactions. The successful synthesis of GaP nanowires without any metallic impurities is beneficial for further exploration of their fundamental properties and applications. © 2001 American Vacuum Society.