The nucleus is one of the most important cellular organelles and molecular anticancer drugs, such as cisplatin and doxorubicin, that target DNA inside the nucleus, are proving to be more effective at killing cancer cells than those targeting at cytoplasm. Nucleus-targeting nanomaterials are very rare. It is a grand challenge to design highly efficient nucleus-targeting multifunctional nanomaterials that are able to perform simultaneous bioimaging and therapy for the destruction of cancer cells. Here, unique nucleus-targeting gold nanoclusters (TAT peptide-Au NCs) are designed to perform simultaneous in vitro and in vivo fluorescence imaging, gene delivery, and near-infrared (NIR) light activated photodynamic therapy for effective cancer cell killing. Confocal laser scanning microscopy observations reveal that TAT peptide-Au NCs are distributed throughout the cytoplasm region with a significant fraction entering into the nucleus. The TAT peptide-Au NCs can also act as DNA nanocargoes to achieve very high gene transfection efficiencies (≈81%) in HeLa cells and in zebrafish. Furthermore, TAT peptide-Au NCs are also able to sensitize formation of singlet oxygen (1O2) without the co-presence of organic photosensitizers for the destruction of cancer cells upon NIR light photoexcitation. A unique nucleus-targeting gold nanocluster(TAT peptide-Au NC)-based multifunctional theranostic platform is designed to perform simultaneous in vitro and in vivo cellular fluorescence imaging, gene delivery, and intrinsic near infrared light-activated photodynamic therapy. This is done without the co-presence of organic photosensitizers for the effective cancer cell killing. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.