Solvent extraction of In(Ⅲ) with versatic acid-10 in sulfuric acid solutions was studied. The distribution coefficient was increased with pH and showed a transition at about pH of 2.4. In the pH range above 2.4 the slope was still less than 3 because of the formation of complexes between indium ions and sulfate ions, and below 2.4 it was much less than 3. The distribution coefficient had a maximum value when the concentration of indium ions in the aqueous phase was 1g/ℓ. It was higher with the versatic acid dissolved in benzene than in keroserne because of the stronger dissociation of the versatic acid in benzene, and was increased with the concentration of versatic acid-10. The enthalpy change of the extraction reaction was found to be 12 Kcal per mole. There was antisynergistic effect in the mixed solvent with TBP but synergism with T.O.P.O. in the pH range of above 24. The McCabe-Thiele diagram showed that five extraction stages with the A/O ratio of 1/4 was required to extract about 99% of indium.