Abstract: The extraction of Np (Ⅳ) and separation of Am (Ⅲ) from Np (Ⅳ) by DHDECMP-DEB in nitric acid medium is described.Experimental results show that equilibrium for Np (Ⅳ) is reached in 30 s. The distribution ratio of Np (Ⅳ) decreases with increase of temperature and increases with concentration of nitric acid and DHDECMP. The enthalpy change △HNP(1v) is estimated to be 15 kJ/mol. The logarithmic plots of DNP(1v)-DHDECMP is a straight line with a slope of 2.0. Therefore, extraction reaction for Np (Ⅳ) with DHDECMP can be expressed as Np4+ +4NO-3 + 2DHDECMP Np(NO3)4·2DHDECMP.The separation of Am from Np can be achieved by means of nitric acid stripping with a separation factor of higher than 50.