Abstract: Vanadium is a strategic metal in many countries, and it is mainly extracted from vanadium slag produced in titanomagnetite metallurgy. The traditional sodium roasting process for vanadium extraction poses environmental threats, and a green calcification process has been proposed. However, the vanadium extraction rate in the calcification process is much lower than in the sodium roasting process, which is related to vanadium solid solubility in Fe₂TiO₅. Previous studies about vanadium behavior in Fe₂TiO₅ were conducted in air, with a vanadium oxidation state of V⁵⁺. Vanadium with lower oxidation states has been detected in the tailings in the calcification process. The present paper studied the effects of vanadium oxidation states on the solid solubility in Fe₂TiO₅ through solid-state reaction, X-ray diffraction characterization, transmission electron microscopy characterization, X-ray photoelectron spectroscopy analysis, and solid solution modeling. The relative interaction values between vanadium oxides and Fe₂TiO₅ are obtained as |L_\textV_2\textO_3| > |L_\textV_2\textO_4| > |L_\textV_2\textO_5| , indicating that vanadium with lower valence is preferable to be solid dissolved in Fe₂TiO₅. The results imply that insufficiently oxidized vanadium increases the vanadium content in the Fe₂TiO₅ phase during vanadium slag’s calcification roasting. Besides, experimental conditions optimization shows that higher experimental temperature, vanadium introduction as V₂O₃, and a high-purity argon atmosphere would lead to higher vanadium solubility in Fe₂TiO₅, and high temperature is beneficial for the release of vanadium from vanadium-containing Fe₂TiO₅ when dissociated in air.