Abstract: Tri-isoamyl phosphate(TiAP or TAP) with tributyl phosphate(TBP) in physical characters, extraction ability and radiation-resist stability were compared. The results show that TiAP is a better extractant than TBP in physical properties, ability of extraction of Np(Ⅳ) and Pu(Ⅳ), and radiation-resist stability. It shows that radiation stability of TiAP is adequate for most of the process application, ability of extraction of Np(Ⅳ), Pu(Ⅳ), U(Ⅵ) and Np(Ⅵ) is good, and the extraction of fission product contaminants such as Zr, Nb, Ru, Cs is almost negligible even at very high nitric acid concentrations in the aqueous phase. TiAP may be an alternative extractant to TBP for extraction and separation of actinide elements, which is especially suitable for systems containing high-level radioactivity and/or high concentration plutonium. It is worthy of further exploration.