Spent vanadium catalysts of sulfuric acid production (main elemental composition in wt%: 7.5 V, 9.1 K, 10.2 S, 23.2 Si and 1.4 Fe) can be used as a secondary source of vanadium. Extraction of vanadium was studied using two-step leaching (acidic and reductive) of spent vanadium catalysts with further oxidizing of leaching solutions. The factors leaching and hydrolysis temperature, concentration of leaching (H₂SO₄, Na₂SO₃) and oxidizing ((NH₄)₂S₂O₈) reagents, solid/liquid ratio, mixing parameters, and time of leaching and thermohydrolysis were systematically investigated. The solubility of V₂O₅ was investigated as a function of temperature, pH of sulfuric acid solutions, and concentration of Na₂SO₃. The kinetics of V₂O₅ solubility and reduction were also studied. The vanadium leaching yield after a two-step recovery was 98 wt% after acidic (H₂SO₄, pH 1.2–1.3) leaching with ultrasonic treatment for 5 min at ambient temperature, followed by reductive leaching in 0.01 Mol/L Na₂SO₃ solution for 15 min at ambient temperature. The highest vanadium extraction yield from leaching solutions was 98 wt% obtained through oxidizing of leaching solutions by 30 wt%. (NH₄)₂S₂O₈ with a molar ratio n(V₂O₅)/n((NH₄)₂S₂O₈) of 5/1 for a reaction time of 5 min at 80–90 °C. the extracted vanadium product was V₂O₅ with a purity of 85–87 wt%. The technological scheme has been developed to recycle all obtained products and sub-products