The stability of organic extractant molecules against radiolysis is critical in the field of actinides and lanthanides (An/Ln) separations. In order to evaluate the radiolytic effects on the extraction performance, the solutions of N,N’-diethyl-N,N’-ditolyl-2,9-diamide-1,10-phenanthroline (Et-Tol-DAPhen) in n-octanol were subjected to γ-irradiation in the presence and absence of 3 mol/L HNO₃ aqueous phase. Et-Tol-DAPhen diluted in n-octanol was almost completely decomposed after irradiation and exhibits decreased extraction ability at an absorbed dose of about 384 kGy, along with the appearance of various degradation products. Et-Tol-DAPhen, which was diluted in n-octanol, was completely decomposed upon irradiation in the presence of 3 mol/L HNO₃ aqueous phase. However, it exhibited higher D_U and SF_U/Eu values than before irradiation, as well as degradation products that were also generated. The structures of some isomers of radiolytic products were investigated by density functional theory (DFT) calculations, the radiolysis pathways and products of Et-Tol-DAPhen extractants were obtained, and the radiolysis pathways and products of Et-Tol-DAPhen extractants was proposed. The radiolytic products mainly originated from amide bond and NC bond cleavage of side group substituents, and some resulted from interaction with n-octanol radicals generated during radiolysis. The presence of HNO₃ can inhibit the radiolysis of Et-Tol-DAPhen to a certain extent and cause enhanced extraction ability. Moreover, the DFT calculations reveal that the radiolytic products produced in presence of 3 mol/L HNO₃ aqueous phase also have efficient extraction performance towards UO₂²⁺. The understanding of the radiolysis pathways and products of extractants, based on radiation chemical effects is expected to be helpful for developing new strategies for extractants with long-term performance.