The growing demand for electric vehicles, driven by global decarbonization policies, has led to an increase in the production of electric steel, which is characterized by a high silicon content. Producing this type of steel necessitates careful control of slag composition, particularly with high SiO2SiO2 content. This study investigates the thermophysical properties of cleanness slags with varying silicon oxide (SiO2SiO2) content, specifically examining viscosityViscosity, surface tensionSurface tension, and densityDensity. Silicon oxide, ranging from 1 to 20 wt%, was added to slags with a CaO/Al2O3Al2O3 ratio of 1. The results show that increasing SiO2SiO2 content raises viscosityViscosity at temperaturesTemperature above 1550 °C but reduces it at lower temperaturesTemperature. Additionally, a linear decrease in densityDensity and surface tensionSurface tension was observed with increasing SiO2SiO2, which is attributed to the substitution of CaO with SiO2SiO2, thereby reducing the number of unsatisfied bonds in the slag network. Understanding these dynamics enhances control over slag-steel interactions in the steel ladle, ultimately improving process efficiency and steel quality.