Abstract: Yttrium and ytterbium were extracted from sulfuric acid medium using triphenylarsine (TPAs) dissolved in kerosene. The influence of different factors, such as shaking time, extractants, metal ions, sulfate ion concentrations, as well as temperature, was studied in detail. From the slope analysis method and IR measurements, the structure of the extracted species was suggested as MSO₄(HSO₄)·TPAs, where M refers to Y(III) or Yb(III). The equilibrium constants (K_ex) and thermodynamic parameters, such as the change in enthalpy (ΔH), free energy (ΔG), and entropy (ΔS), were calculated. The method of extraction and stripping was applied to obtain the aforementioned metals from a sample of fluorspar mineral giving a recovery yield of 88.2% and 83.5% for yttrium and ytterbium, respectively.