Gallium nitride (GaN) nanowires were synthesized using the recently developed oxide-assisted method by laser ablating a target of GaN mixed with gallium oxide (Ga2O3). Transmission electron microscopic characterization showed that GaN nanowires were smooth and straight with a core-sheath structure of 80 nm in average diameter and tens of micrometers in length. Both hexagonal and cubic structured GaN nanowires were produced. The growth mechanism was discussed.