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The β−-particle-emitting erbium-169 is a potential radionuclide toward therapy of metastasized cancer diseases. It can be produced in nuclear research reactors, irradiating isotopically-enriched 168Er2O3. This path, however, is not suitable for receptor-targeted radionuclide therapy, where high specific molar activities are required. In this study, an electromagnetic isotope separation technique was applied after neutron irradiation to boost the specific activity by separating 169Er from 168Er targets. The separation efficiency increased up to 0.5% using resonant laser ionization. A subsequent chemical purification process was developed as well as activity standardization of the radionuclidically pure 169Er. The quality of the 169Er product permitted radiolabeling and pre-clinical studies. A preliminary in vitro experiment was accomplished, using a 169Er-PSMA-617, to show the potential of 169Er to reduce tumor cell viability. © Copyright © 2021 Talip, Borgna, Müller, Ulrich, Duchemin, Ramos, Stora, Köster, Nedjadi, Gadelshin, Fedosseev, Juget, Bailat, Fankhauser, Wilkins, Lambert, Marsh, Fedorov, Chevallay, Fernier, Schibli and van der Meulen. The authors thank CERN ISOLDE and RILIS teams for the laser operation (Maxim D. Seliverstov, Katerina Chrysalidis), radiation protection and logistic teams of PSI (Tobias Schneider) and CERN (Alexandre Dorsival, Matthieu Deschamps and Elodie Aubert, Philippe Bertreix, Nicolas Riggaz, Nabil Menaa, Aurore Boscher, Jeremie Comte, Benjamin Juif); the LARISSA workgroup of Mainz University for the laser preparation and erbium laser ionization scheme development (Prof. Dr. Klaus Wendt and Dr. Dominik Studer). The authors are grateful to Fan Sozzi-Guo, Muhamet Djelili, Alexander V?gele and Walter Hirzel (PSI) and Bernard Cr?pieux, Giacomo Lunghi, Francesco Riccardi, Miranda Van Stenis, Thomas Schneider (CERN) for technical support. Funding. ZT and NM received funding from the Swiss National Science Foundation (SNF Grant Number: 200021_188495). CM obtained funding for this project from the Swiss Cancer Research (KFS-4678-02-2019-R). FB received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Sk?odowska-Curie Grant Agreement No 701647.