The molten rare earth salt for refining impure-red-copper was performed. It is determined that the molten RE salt is mainly composed of RECO 3
Na 2CO 3
CaF
metallic oxide (MO) and Na 2B 4O 7. The optimum composition of molten RE salt refiner was obtained by orthogonal experiment. The results show that the refiner can improve the electric conductivity of refined impure-red-copper up to 99.6% IACS with oxygen content in top level.