This paper aimed to find an effective method to destroy cancer cells by targeting breast cancer cells with natural killer (NK) cells transfected with the human ferritin heavy chain (hFTH1) gene by polyethylene glycol (PEG)-modified dendrimerentrapped gold nanoparticles (Au DENPs). In this study, fifth-generation polyamidoamine (G5 PAMAM) dendrimers modified with PEG were used as templates to entrap gold nanoparticles to transfect hFTH1 into NK cells. Our results revealed that the prepared Au DENPs/FTH1 provided high-quality imaging performance (hypointensity on T2-weighted MR imaging) and efficient transfection efficiency (reaching 80.2%) at a N/P ratio (ratio of the number of surface primary amines on {(Au0)25-G5 · NH₂-mPEG17} to the number of phosphate groups in the hFTH1 backbone) of 5:1. Interestingly, the results showed that Au DENPs/FTH1 effectively guided NK-92 cells to concentrate around tumor cells for effective gene therapy without severely impacting their activity. This work will provide a new research platform for immunotherapy based on NK cells and lead to the optimization and even individualization of breast cancer immunotherapy through nanomolecular visualization research, which has a broad scope for future clinical applications.