unassigned: Recently, nanocatalyst-induced endoplasmic reticulum (ER) stress for cancer therapy has been attracting considerable attention. However, cancer cells are often able to overcome ER stress-induced death by activating the unfolded protein response (UPR), making nanocatalytic monotherapy a poor defense against cancer progression. unassigned: In this study, to improve the nanocatalytic treatment efficacy, a phase change material (PCM) was used to encapsulate the upstream ER stress initiator, iron oxide nanoparticles (FeO NPs), and the downstream UPR modulator, PR-619. Subsequently, the tumor-homing peptide tLyP-1 was coupled to it to form tLyP-1/PR-619/FeO@PCM (tPF@PCM) theranostic platform. unassigned: tPF@PCM was synthesized using nanoprecipitation and resolidification methods followed by the EDC/NHS cross-linking method. The targeting capacity of tPF@PCM was evaluated in vitro and in vivo using flow cytometry and magnetic resonance imaging, respectively. The therapeutic efficacy of tPF@PCM was investigated in a renal cell carcinoma mouse model. Moreover, we explored the synergistic anti-tumor mechanism by examining the intracellular reactive oxygen species (ROS), aggregated proteins, ER stress response levels, and type of cell death. unassigned: tPF@PCM had excellent tumor-targeting properties and exhibited satisfactory photothermal-enhanced tumor inhibition efficacy both in vitro and in vivo. Specifically, the phase transition temperature (45 °C) maintained using 808 nm laser irradiation significantly increased the release and catalytic activity of the peroxidase mimic FeO NPs. This strongly catalyzed the generation of hydroxyl radicals (•OH) via the Fenton reaction in the acidic tumor microenvironment. The redox imbalance subsequently resulted in an increase in the level of damaged proteins in the ER and initiated ER stress. Moreover, the pan-deubiquitinase inhibitor PR-619 blocked the "adaptive" UPR-mediated degradation of these damaged proteins, exacerbating the ER burden. Consequently, irremediable ER stress activated the "terminal" UPR, leading to apoptosis in cancer cells. unassigned: This ER stress-exacerbating strategy effectively suppresses tumorigenesis, offering novel directions for advances in the treatment of conventional therapy-resistant cancers.