The synthesis of gallium oxide and nitride nanocrystals is challenging. Herein, a forced hydrolysis route is developed to synthesize α-GaOOH and the morphology control of nanocrystals is realized by adjusting the ratios of ionic strength in the synthesis system. The as-prepared α-GaOOH nanorods can be transformed into α-Ga₂O₃ nanorods upon calcination and can be further transformed into GaN nanocrystal assemblies through nitridation at elevated temperatures, which provides a top-down strategy to gallium oxide and nitride nanocrystals. The synthesis results are investigated by means of X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The optical properties, i.e. ultra-violet visible absorption (UV-vis) and photoluminescence, of as-obtained α-Ga₂O₃ nanocrystals with different morphologies are examined and the morphology–property relationship is discussed.