Hexagonal GaN micro-ribbons were synthesized through nitriding Ga2O3 films under flowing ammonia. Ga2O3 films were deposited on the Ga-diffused Si (111) substrates by radio frequency (r.f.) magnetron sputtering. X-ray diffraction (XRD), scanning electron microscopy (SEM), selected area electron diffraction (SAED); X-ray photo electronic spectrometer (XPS) and photoluminescence (PL) spectroscopy were used to characterize the structure, surface morphology, composition and optical property of the synthesized samples. SEM images show that GaN micro-ribbons with 100-300rim in diameter are randomly distributed on the uniform films. XRD, XPS and SAED analysis suggest the micro-ribbons are polycrystalline GaN with hexagonal structure and preferentially grow in the [001] direction. The PL spectrum has a remarkable blue shift compared with the reported values of bulk GaN, which might be ascribed to quantum confinement effects.