The dissolution of TiO2 in the CaO-Al2O3-SiO2 slag under static conditions was studied in the temperature range from 1643 K to 1703 K. After TiO2 dissolved, the microstructure of the interface between TiO2 and the slag was observed by scanning electron microscopy, and the concentration profiles of Ti4+ and other ions across the TiO2/slag interfaces were analyzed by energy-dispersive X-ray spectroscopy. On the basis of these results, the dissolution behavior of TiO2 was evaluated, and the diffusivity of Ti4+ in the bulk slag was estimated. According to the Stokes–Einstein relation, the viscosity calculated by a previously reported model gave a diffusivity of Ti4+ ions greater than that estimated by the concentration profiles of Ti4+ ions. The mechanism of TiO2 dissolution in the CaO-Al2O3-SiO2 slag is discussed in detail. The dissolution of TiO2 in the CaO-Al2O3-SiO2 slag under static conditions was studied in the temperature range from 1643 K to 1703 K. After TiO2 dissolved, the microstructure of the interface between TiO2 and the slag was observed by scanning electron microscopy, and the concentration profiles of Ti4 + and other ions across the TiO2 / slag interfaces were analyzed by energy-dispersive X-ray spectroscopy. On the basis of these results, the dissolution behavior of TiO2 was evaluated, and the diffusivity of Ti4 + in the bulk slag was estimated. According to the Stokes-Einstein relation, the viscosity calculated by a previously reported model gave a diffusivity of Ti4 + ions greater than that estimated by the concentration profiles of Ti4 + ions. The mechanism of TiO2 dissolution in the CaO-Al2O3-SiO2 slag is discussed in detail