A study of liquid-liquid extraction behavior of gallium (III), indium (III), and thallium (III) with Cyanex-925 (Bis-2,4,4-trimethyl pentyl-n-octyl phosphine oxide) was undertaken. Both gallium (III) and indium (III) were coextracted in the pH range 4.0-5.0 while thallium. (III) was extracted between pH 2.0 and 4.0. The gallium, indium, and thallium ions were stripped out from the organic phase with 1.0 mol/L HNO3, 1.5 mol/L HCl, and 3.0 mol/L HCl, respectively. The optimum conditions of extractability were found separately as functions of pH, temperature, equilibrium time, and stripping ability. Based on these results, a sequential method was developed for the separation of gallium (III), indium (III), and thallium (III).