Abstract: The retention of RuNO complexes in irradiated solvent is small for 30%TBP-kerosene, TBP and Kerosene which are not pre-equilibrated with HNO_3before irradiation. If They are pre-equilibrated with mol/l HNO_3, the retentionin kerosene or TBP is small too. The retention in 30% TBP-kerosene increaseswith the radiation dose. The retention of Ru in irradiated TBP-kerosene increase, with the concentrationof pre-equilibrating nitric acid and the ageing time after ruthenium extraction.After washing with 2 mol/l HNO_3 and 0.5 mol/l sodium carbonate at 30℃, theretention is large. After irradiation, the solvent is separated into Na_2CO_3 extract,H_2O extract and neutral phase by Becker's Method. Thc retention of Ru in H_2Oextract is smaller. But the retention of Ru in neutral phase is quite large.