The influence of Al2O3 in the range of 10–20 mass% and TiO2 in the range of 0.55–5 mass% on the flow behavior, viscosity, density, and surface tension of molten industrial blast furnace slag with CaO/SiO2 = 1.13 is investigated using a high‐temperature microscope, a rotating viscometer, and the maximum bubble pressure method. The measurement results show that Al2O3 acts as a network former in the studied CaO–SiO2–MgO–Al2O3–TiO2 slags. With an increase in the Al2O3 content from 10 to 20 mass%, the viscosity and surface tension of the slags increase and the density decreases. In contrast to Al2O3, the TiO2 acts as a surfactant and network breaker in the range of up to 15 mass%. The addition of TiO2 up to 15 mass% results in a decrease in the viscosity in the liquid‐dominated region and a decrease in the surface tension of the studied slags. Therefore, the density increases with the addition of TiO2 due to increasing molar volume. The behavior of the breakpoint temperature on all the viscosity curves is in complete agreement with the behavior of the flow point temperature and crystallization temperatures of melilite and perovskite.