While the current standard first-line treatment for advanced renal cell carcinoma (RCC) is sunitinib, patients inevitably develop resistance to this drug. However, the rapid development of nanotechnology has provided emerging techniques for the treatment of advanced tumours, including RCC. In our previous research, cuprous oxide nanoparticles (CONPs) showed ideal anti-tumour effects and low systemic toxicity. While many inorganic nanomedicines, including CONPs, have similar pharmacological effects, their detailed mechanisms remain unknown. Copper chaperone proteins, which regulate the endocellular dosage and transport of copper, also play crucial roles in the progression of cancer. In this research, we discovered that CONPs can disrupt copper transportation by regulating the copper chaperone proteins ATOX1 and CCS in RCC cells and induce endoplasmic reticulum (ER) stress in?vitro and in?vivo by promoting the accumulation of intracellular calcium and reactive oxygen species (ROS). Furthermore, CONPs can initiate ER- and mitochondrial-dependent apoptosis by activating caspase-3, caspase-9 and caspase-12. In addition, CONPs downregulate the expression of AXL, MET, AKT, and ERK to recover sunitinib responsiveness in RCC cells with sunitinib resistance (SR) and may therefore facilitate the development of promising new pathways to treat patients with acquired SRRCC.