Abstract: The effects of TiO₂ content, Al₂O₃ content and binary basicity (CaO/SiO₂) on the viscosity of a TiO₂-Al₂O₃-CaO-SiO₂ fully liquid slag with high TiO₂ content and low mass ratio of CaO to SiO₂ were studied in this paper. Experimental determinations of the viscosity were carried out in the temperature range from 1633 to 1873 K using the rotation cylinder method. When the TiO₂ content is from 23% to 43%, the Al₂O₃ content is from 3% to 12%, and the binary basicity is from 0.3 to 0.7, the viscosity of the slag decreases with increasing TiO₂ content and alkalinity, but increases with increasing Al₂O₃ content. TiO₂ is classified as an acidic oxide by calculating the sulfur partition rate of the slag in the electric furnace melting process. Based on the data of viscosity measurement and the definition of TiO₂ attributes, a new melt viscosity prediction model of the slag was proposed by modifying the Urbain model. Its prediction error is 11%, indicating that the model provides a reasonable prediction for fully liquid slags with high TiO₂content and low mass ratio of CaO to SiO₂.