Abstract: Aiming at the process of smelting ultra-high (>80%) or even full vanadium titanomagnetite in blast furnace, we are conducting a series of works on physics character of high TiO₂ bearing blast furnace slag (BFS) for slag optimization. This work discussed the density and surface tension of high TiO₂ bearing BFS using the Archimedean principle and the maximum bubble pressure method, respectively. The influence of TiO₂ content and the MgO/CaO mass ratio on the density and surface tension of CaO–SiO₂–TiO₂–MgO–Al₂O₃ slags were investigated. Results indicated that the density of slags decreased with the TiO₂ content increasing from 20wt% to 30wt%, but it increased slightly with the MgO/CaO mass ratio increasing from 0.32 to 0.73. In view of silicate network structure, the density and the degree of polymerization (DOP) of network structure have a consistent trend. The addition of TiO₂ reduced (Q³)²/(Q²) ratio (Q² and Q³ represent structural unit with bridge oxygen number of 2 and 3, respectively) and then decreased DOP, which led to the decrease of slag density. The surface tension of CaO–SiO₂–TiO₂–MgO–Al₂O₃ slags decreased dramatically with the TiO₂ content increasing from 20wt% to 30wt%. Conversely, it increased with the MgO/CaO mass ratio increasing from 0.32 to 0.73. Furthermore, the iso-surface tension lines were obtained under 1723 K using the Tanaka developed model in view of Butler formula. It may be useful for slag optimization of ultra-high proportion (>80%) or even full vanadium titanomagnetite under BF smelting.