The rising incidence of cancer has heightened interest in immune cell therapy, particularly the role of natural killer (NK) cells, which are essential components of the immune system. Their applications in tumor treatment have expanded significantly, especially with the incorporation of nanomaterials. This review comprehensively examines NK cell biology, encompassing aspects such as classification, distribution, receptor activation, and mechanisms of cytotoxicity. It also explores various NK cell therapies, including their sources, methods of acquisition, expansion techniques, Chimeric antigen receptor-Natural Killer cell (CAR-NK) technology, gene editing strategies, and combination therapies. Additionally, the review discusses the utilization of nanomaterials in NK cell therapy, focusing on nanoparticle-assisted immune regulation and the modulation of the tumor microenvironment. While NK cell therapy holds promise, CAR-NK technology presents certain limitations. The integration of nanomaterials offers potential strategies to enhance therapeutic efficacy. Future research should prioritize the optimization of NK cell therapy, address the limitations associated with CAR-NK technology, investigate the mechanisms of nanomaterials, and develop more effective nanomaterials to improve clinical outcomes.