Abstract: A method of uranium isotope enrichment by utilizing a photochemically selective effect is provided. The method comprises placing a powder of a uranyl compound of carboxylate having at least one oxygen-containing substituent in a magnetic field, irradiating the powder for an effective period of time with visible or shorter wavelength light capable of being absorbed by uranyl ion in the uranyl compound, and separating the resulting reduction products of the uranyl ion from the unreacted uranyl compound by fractionation to isolate a fraction enriched with .sup.235 U isotope. An ordinary light source having wavelengths of a wide range can be used, and there is no need for uranium gasification and cryogenic cooling which are required in a conventional laser method or molecular laser method.