Abstract: In investigating the extraction capacities of U(Ⅳ) by 31 crown ethers with various substituting groups from hydrochloric acid, it is found that U(Ⅳ) is not extracted at 5.5M HC1 by dicyclohexyl-crown ethers, but distribution ratios of U(Ⅳ) increase quickly when HC1 concentration is increased to 6-8.5M HC1. The species extracted are identified as H2UC18·2DCH, DCH being dicyclohexyl-crown ethers. The extraction ability of uranium by five DCH decreases in the order: DCH-27C9>DCH-24C8>DCH-18C6>>DCH-30C10> DCH-21C7. DCH could be a useful reagent for the separation of U(Ⅵ) from U (Ⅳ).