The thermostability and reactivity of GaP nanocrystals in O-2 were investigated using the thermogravimetric analysis (TGA), differential thermal analysis (DTA), powder X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) analysis techniques. alpha-Ga2O3 nanoparticles, nano-hollow-particles, or nanorods and nanotubes can be separately obtained from the oxidation of nanocrystalline GaP at 400 degreesC for 30 min in dry O-2 atmosphere via manipulating different heating rates. Transmission electron microscopy (TEM) and energy-dispersive X-ray spectrometry (EDX) analysis showed that the products were all alpha-Ga2O3 but with different morphologies when different heating rates were applied. The formation mechanisms of the different morphological alpha-Ga2O3 nanocrystals were discussed.