This paper reports the use of impregnated polyurethane foam for enriching trace thorium from natural water, The polyether type polyurethane form was employed, which was impregnated with bis (2-ethylhexyl) phosphoric acid, tributyl phosphate/carbon tetrachloride (2:5:93, V/V/V) mixture, The excess reagent was removed by filter paper, The impregnated foam thus prepared is dipped into the water sample and stirred for 20 minutes, The optimum conditions for enrichment are.sample should.be adjusted to about pH 1 and temperature should be kept.within 30-45℃, Distribution and phase ratios were calculated to be 4,26×10⁴ and 2.01×10⁴ respectively, assuming that the mixture and water are totally immiscible with each other, The actual values were all slightly greater than the calculated ones, After removing the foam from the sample, the former is washed with water and subjected to wet oxidation with concentrated nitric and perchloric acids.The residue is taken up with diluted hydrochloric said, The thorium is spectrophotometrieally determined with Arsenazo 111 at 665 nm.The method is simple, rapid, accurate and inexpensive.