Abstract: The retention of the nitrato complexes of nitrosylruthenium by the irradiated TBP-n-dodecane HNO₃ is studied. The extraction equilibrium time of the nitrato complex of nitrosylruthenium by the irradiated TBP-n-dodecane-HNO₃ and the washing equilibrium time by sodium carbonate were determined. The distribution coefficients of ruthenium by several model radiolysis products were determined. The effects of absorbed dose, the nitric acid concentration of the nitrosylruthenium nitrato complex, the nitric acid concentration for preequilibration with TBP before irradiation, ruthenium extracted by the TBP-n-dodecane-HNO₃ before irradiation on Ru retention percent were studied by phase ratio variation method. The results show that the extraction equilibrium time is quite long. The wash equilibrium time by sodium carbonate is faster. The Ru retention in irradiated TBP-extraction system increases with absorbed dose, the concentration of preequilibrating nitric acid before irradiation, and the cycle number. The Ru retention is larger when Ru is extracted by the TBP-n-dodecane-HNO₃ before irradiation. The organic phase is placed for several days after Ru is extracted by the irradiated TBP-n-dodecane-HNO₃. The Ru retention increases when the aging time is one day then gradually decreases. The Ru retention is small when there is no diluent or nitric acid in the extraction system before irradiation. The Ru retention changes little with the aging time of the irradiated TBP-n-dodecane-HNO₃ and the concentration of extracting nitric acid. Nitric organophosphates are the main complexing agents that can coordinate with Ru.