Taguchi's method was used to determine the optimum conditions for the separation of uranium and thorium using neutral extractants. The experimental conditions were studied in the concentration ranges of 0.01-5 M for three different acids (nitric acid, hydrochloric acid, and sulfuric acid) using tributylphosphate (TBP), trioctylamine (TOA), and tricaprylyl methyl ammonium chloride (Aliquat 336) as the extractants. The optimum condition for the separation of thorium from uranium was obtained at 5.0 M nitric acid solution using Aliquat 336. Under this condition, thorium was extracted selectively from uranium with the extraction efficiency and separation factor of 97.5% and 33.07, respectively. The equilibrium equations were also determined. The results showed that the optimum combination for uranium was extraction from 2.0 M hydrochloric acid solution by Aliquat 336. (C) 2013 Elsevier Ltd. All rights reserved.