INTRODUCTION: Natural Killer (NK) cells have attracted extensive attention as therapeutic agents for hematological malignancies and solid tumors. NK cell therapies carry a lower risk of Graft-Versus-Host Disease (GVHD) in allogeneic transplantation, making them ideal candidates for "off-the-shelf" allogeneic cell therapies. However, the expansion culture of NK cells typically employs a scale-out strategy using a large number of culture vessels, making it still challenging to use NK cells as 'off-the-shelf' allogeneic cell therapies. While scalable, aerated stirred bioreactor could be an ideal approach, there have been no reports on culture evaluations specifically targeting iPCS-derived NK cells. METHODS: We developed a process for expanding iPCS-derived NK cells using a stirred culture system. The NK cell stimulation process with agonist antibodies and expansion process were repeated, and the cell expansion and quality of iPCS-derived NK cells were evaluated. Scale-up factors were evaluated using an aerated stirred bioreactor, and process scale-up was performed from 1 L to 10 L bioreactors. RESULTS: iPCS-derived NK cells showed higher cell expansion in stirred cultures than in static cultures. By repeated stimulation and expansion processes, iPCS-derived NK cells expanded 1000-fold with comparable cell expansion and quality. iPCS-derived NK cells could be scaled up from 1 L to 10 L aerated stirred bioreactors with comparable cell expansion and quality. CONCLUSIONS: Through systematic process evaluation and optimization, we demonstrated that iPCS-derived NK cells can be expanded in a scalable aerated stirred bioreactor.