Abstract: The composition, distribution and microtopography of titaniferous inclusions in Ti-IF steel during steelmaking and in the casting billets were investigated systematically, and the evolution of the titaniferous inclusions was described subsequently. Both thermodynamic analysis and experimental results indicate that TiN could not precipitate in the steelmaking process, while the titaniferous inclusions exist in the form of a combination of titanium oxides which mainly consists of TiO₂ and other oxides. In the solidification process of continuous casting, TiN inclusions precipitate in the heterogeneous nucleation way due to the decrease of liquid steel temperature and the segregation effect. The main non-metallic inclusions in the casting billets are large size Al₂O₃ particles and TiN-Al₂TiO₅-Al₂O₃ triple-layer complex inclusions with the middle layer of Al₂TiO₅. The nucleation and growth process of TiN-Al₂TiO₅-Al₂O₃ complex inclusions is that[Al],[Ti] and[N] form the middle layer of Al₂TiO₅ firstly on the Al₂O₃ core surface, then TiN nucleates and grows up on the Al₂TiO₅ surface. Since TiN inclusions in the casting billets are difficultly removed during the steelmaking process, it is feasible to control titaniferous inclusions in the steel by inclusion modification.