A selective and very effective separation method for uranium(VI) has been developed by using poly(dibenzo-18-crown-6) and column chromatography. The separations are carried out from ascorbic acid medium. The adsorption of uranium(VI) was quantitative from 0.00002 to 0.006 M ascorbic acid. The elution of uranium(VI) was quantitative with 2.0-8.0 M HCl and 2.0-5.0 M H 2 SO 4 . The capacity of poly(dibenzo-18-crown-6) for uranium(VI) was found to be 0.92+/-0.01 mmol g - 1 of crown polymer. Uranium(VI) was separated from a number of cations in binary as well as in multicomponent mixtures. The method was extended to the determination of uranium in geological samples. It is possible to separate and determine 5 ppm of uranium(VI) by this method. The method is very simple, rapid, selective and has good reproducibility (approximately +/-2%).