The effect of nitrogen concentration on the interfacial and optical properties, as well as band offsets of HfTiO thin films by rf sputtering HfTi alloy target has been systematically investigated. The results indicate that an interfacial layer is unavoidably formed between HfTiON thin films and Si substrate, and the main content of the interfacial layer is silicate. No silicide is formed in the interfacial layer which is partly responsible for the poor electrical properties of high-k gate dielectrics. The optical properties of HfTiON films change, such as the refractive index decreases, while the extinction coefficient increases with the increase of N content, due to the defects increase in the films. The results also indicate that the bandgap and VB offset reduce with the introduction of N into HfTiO thin films. The CB offset of the HfTiON thin films is almost unchanged indicating that the N concentration has little effect on CB offset. However, the bandgap and band offsets are all higher than 1 eV, the sufficient band offsets still makes sputtering-derived HfTiON films by HfTi alloy target a promising high-k gate dielectric for future complementary metal oxide semiconductor technology.