Abstract: The viscosity of CaF₂-CaO-Al₂O₃-MgO-(TiO₂) slag was measured using a rotating crucible viscometer. Raman spectroscopy analysis was performed to correlate the viscosity to slag structure. The viscosity of the slag was found to decrease with increasing TiO₂ content in the slag from 0 to 9.73wt%. The activation energy decreased from 95.16 kJ/mol to 79.40 kJ/mol with increasing TiO₂ content in the slag. The introduction of TiO₂ into the slag played a destructive role in Al-O-Al structural units and Q⁴ units by forming simpler structural units of Q² and Ti₂O₆^4- chain. The amount of Al-O-Al significantly decreased with increasing TiO₂ content. The relative fraction of Q⁴ units in theAlO₄^5--tetrahedral units shows a decreasing trend, whereas the relative fraction of Q² units and Ti₂O₆^4- chain increases with increasing TiO₂ content accordingly. Consequently, the polymerization degree of the slag decreases with increasing TiO₂ content. The variation in slag structure is consistent with the change in measured viscosity.