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 ¹⁶⁸ Er ₂ O ₃ . 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 ¹⁶⁹ Er from ¹⁶⁸ Er 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 ¹⁶⁹ Er. The quality of the ¹⁶⁹ Er product permitted radiolabeling and pre-clinical studies. A preliminary in vitro experiment was accomplished, using a ¹⁶⁹ Er-PSMA-617, to show the potential of ¹⁶⁹ Er to reduce tumor cell viability.