Solvent extraction studies on protactinium were carried out from hydrofluoric acid, hydrochloric acid, and a mixture of hydrochloric and hydrofluoric acids using Aliquat 336 and Pa-231. The extraction of protactinium from hydrofluoric acid (0.025-10 M) decreased with increasing acid concentration and was less than 10% above 5 M. The extraction from hydrochloric acid (0.5-8 M) started only above 4 M and increased with increasing acid concentration. The extraction of protactinium from a mixture containing hydrochloric acid (0.5-8 M) and 0.03 M hydrofluoric acid decreased with increasing acid concentration reached to a minimum at about 2 M and then increased with increasing acid concentration. At low acidity, extraction of protactinium from hydrofluoric acid was higher compared to hydrochloric acid and the mixture of hydrochloric and hydrofluoric acids. Nitric acid (10 M) and hydrofluoric acid (10 M) were suitable for quantitative recovery of protactinium from organic phase. The extraction of Pa-231 from real thorium lean raffinate of thorium-uranium extraction process was studied using optimized extraction conditions.