'!be equilibrium distribution of dysprosium nitrate, erbium nitrate, and nitric acid between water and tributyl phosphate was studied in this research. Separate equilibrium data were obtained for the distribution of dysprosium nitrate-nitric acid, erbium nitrate-nitric acid, and dysprosium nitrate-erbium nitrate-nitric acid mixtures. The equilibrium data were obtained by making single stage extractions from aqueous feed solutions using commercial grade tributyl phosphate. Equilibrium distribution of solutes was determined by analysis of each phase from the single stage extractions.