Nitridated \beta-Ga2O3 (100) substrate was investigated as the substrate for GaN epitaxial growth. The effects of nitridation temperature and surface roughness of \beta-Ga2O3 wafers on the formation of GaN were studied. It was found that the most optimized nitridation temperature was 900 oC, and hexagonal GaN with preferred orientation was produced on the well-polished wafer. The nitridation mechanism was also discussed.