^​177Lu has sprung as a promising radionuclide for targeted therapy. The low soft tissue penetration of its β⁻ emission results in very efficient energy deposition in small-size tumours. Because of this, ¹⁷⁷Lu is used in the treatment of neuroendocrine tumours and is also clinically approved for prostate cancer therapy. In this work, we report a separation method that achieves the challenging separation of the physically and chemically identical nuclear isomers, ^177mLu and ¹⁷⁷Lu. The separation method combines the nuclear after-effects of the nuclear decay, the use of a very stable chemical complex and a chromatographic separation. Based on this separation concept, a new type of radionuclide generator has been devised, in which the parent and the daughter radionuclides are the same elements. The ^177mLu/¹⁷⁷Lu radionuclide generator provides a new production route for the therapeutic radionuclide ¹⁷⁷Lu and can bring significant growth in the research and development of ¹⁷⁷Lu based pharmaceuticals.