The distribution of Th(IV) between aqueous sulphuric acid and organic phases of N-n-octylaniline in xylene is described. The dependence of the metal extraction on acidity and extractant concentration is investigated. Based on the results obtained, the possible extraction mechanism is discussed. The determination of Th(IV) and its separation from synthetic mixtures is suggested. The method is extended to the analysis of thorium in monazite and gas mantles.