The sample solution in 2 N nitric acid tnediurn was extracted with trioctyl- phosphine oxide (TOPO) in cyclo,hexane solution in the present of ascobic acid, boric acid and aluminium salts, and backextracting with 2 N-HN03 contain ing 0.8% NH4F solution. Uranium was determined in TOPO layer with 5-Br- PADa1P, and thorium was determined in aqueous solution with arsenazo III.Its C. V. for sample containing 1.3ppm U and 1.6ppm Th were 9·0% and 3 .6% respectively (n=8).