Significance Humanized mice represent a promising approach to study the human immune system in health and disease. However, insufficient development and function of human lymphocytes limit the applicability of humanized mice for cancer biology and therapy. We demonstrate that human SIRPA and IL15 knock-in (SRG-15) mice support efficient development of circulating and tissue-resident natural killer (NK) cells, intraepithelial lymphocytes, and innate lymphoid cell subsets. In contrast to previous humanized mouse models, human NK cells in SRG-15 mice mediate efficient antibody-dependent cellular cytotoxicity and thereby enable NK cell-targeted cancer immunotherapy of tumor xenografts. As such, SRG-15 humanized mice may facilitate translational research by enabling the development of novel NK and CD8 ⁺ T cell-based therapeutic approaches that target human infections and malignancies.