β-GaN nanocrystalline have been successfully synthesized from the nitridation of GaP nanocrystalline at low temperatures by gas_phase chemical reaction. The s tarting GaP nanocrystalline has a large specific surface and a high reactivity that can reduce remarkably the difficulty of nitridation. The results of GaP nan ocrystalline in N2 at different heating rates support the fact that β-GaN nan ocrystalline can form in GaP nanocrystalline via N-P metathesis gas_phase chemic al mechanism. The mechanism is different when different heating rate was used. T his method is very simple and is used generally to synthesize β-GaN nanopartic les or nanorods.