Abstract: In tire-cord steel, the deformation behavior of oxide inclusions is primarily influenced by their inherent properties, and fundamentally, it is decided by their structural characteristics. The deformation of oxide inclusions during a four-pass industrial hot-rolling process was investigated using an automatic scanning electron microscope. Subsequently, the corresponding properties and structures of the oxide inclusions in the rolled rods were analyzed using FactSage software and an analytical model. During the hot-rolling process, different types of inclusions exhibited varying deformation behaviors. Specifically, CaO-MnO-Al₂O₃-SiO₂-type inclusions demonstrated the highest deformation index across multiple rolling passes. When the content of SiO₂ reached 70 wt.%, MnO-Al₂O₃-SiO₂- or MnO-SiO₂-type inclusions exhibited non-deformability, similar to SiO₂-type inclusions. These non-deformable inclusions were characterized by high liquidus temperatures (1600-2200 °C) and high viscosities (20-35 ln(Pa s)). Interestingly, the high proportion of bridging oxygen within the oxide inclusions indicated that crystallization was not the primary factor influencing their deformation. The liquidus temperature and viscosity of oxide inclusions maintained an inversely proportional relationship with their aspect ratio. The parameter, D_ratio, was introduced to quantify the degree of depolymerization in the oxide system of tire-cord steel. The reason for the excellent deformability of low-liquidus-temperature inclusions lay in their high D_ratio, which resulted in a more flexible structure. Additionally, higher (CaO + MnO)/SiO₂ ratio correlated with a higher D_ratio and, consequently, lower viscosity.