Abstract: The extraction of Neptunium (Ⅳ) by ten crown ethers with various substituting groups from nitric acid solution have been investigated. The ten crown ethers studied are: Octamethylperhydrocyclotetrafurfurylene, Benzo-15-crown-5, 4-t-butyl-benzo-15-crown-5, 16-crab-5, 18-crown-6, Dibenzo-18-crown-6, Dicyclohexo-18-crown-6, Dibenzo-24-crown-8, Dibenzo-30-crown-10 and Cryptand-222.Experimental results show that there exists some relation between extraction of Neptunium (Ⅳ) with the structure of corresponding complexes in the organic phase, structure of various substituting groups on the rings of macro cyclic polyethers and the concentration of nitric acid in aqueous phase.Among the ten crown ethers, Dicyclohexyl-18-crown-6 has excellent performance. Effects of several solvents were also studied: Benzene, Toluene, o-Xylene, 1,3,5-trime-thylbenzene, Nitrobenzene, n-Hexane, Kerosene, Cyclohexane, Chloroform, 1,2-Dichloro-ethane and Carbon tetrachloride. It is noted that good extraction of Neptunium (Ⅳ) with crown ethers may be effected by using the solvent of high dielectric constant as diluent, such as 1,2-Dichloroethane and Nitrobenzene. The distribution coefficient of Neptunium (IV) by Dicyclohexyl-18-crown-6/1,2-dichloroethane from nitric acid system were studied as a function of the diluent, concentration of crown ethers, acidity in aqueous phase, effects of salting-out agent (NH4+, Na+, Ca2+, Al3+) and so on.The distribution coefficients of 14 radionuclides 144Ce (Ⅳ), 134Cs, 22Na,140Ba, 152Eu, 95Zr-95Nb, 106Ru, 45Ca,90Sr-90Y, 233U (Ⅳ), 232Th (Ⅳ), 237Np(Ⅳ) have also been determined at 18 ± 1℃, and the separation coefficients of Neptunium (Ⅳ) and correspoding radionuclides have been calculated.It seems that DicyclohexyI-18-crown-6 could be a useful reagent for separating Neptunium (Ⅳ) from other radionuclides in the liquid-liquid extraction method.