This study explores the development of a peptide-ferriporphyrin conjugate (Gi-F-CAA) that enhances tumor penetration, endocytosis, and GPX4 inhibition through in vivo self-assembly, ultimately improving anticancer activity via ferroptosis. The Gi-F-CAA is composed of a GPX4 inhibitory peptide, a pH-sensitive peptide linker decorated with cis-aconitic anhydride (CAA), and ferriporphyrin. Under the acidic microenvironment of tumors, the CAA hydrolyzes, leading to the self-assembly of Gi-F-CAA into large nanoparticles (Gi-F). This process enhances tumor endocytosis and GPX4 inhibition due to the assembly-enhanced binding (AEB) effect, increasing the reactive oxidative species (ROS) produced by the Fenton reaction. In vitro and in vivo experiments demonstrate that Gi-F-CAA exhibits enhanced cytotoxicity and tumor accumulation, leading to significant tumor growth inhibition in multiple models, including bladder cancer, multidrug-resistant breast cancer, and large renal cell carcinoma. The study also highlights the potential of Gi-F-CAA in addressing drug resistance and treating large tumors, with excellent biocompatibility and no significant toxicological effects. This work provides a promising strategy for overcoming chemoresistance and improving the therapeutic efficacy of ferroptosis-based cancer therapy.This study explores the development of a peptide-ferriporphyrin conjugate (Gi-F-CAA) that enhances tumor penetration, endocytosis, and GPX4 inhibition through in vivo self-assembly, ultimately improving anticancer activity via ferroptosis. The Gi-F-CAA is composed of a GPX4 inhibitory peptide, a pH-sensitive peptide linker decorated with cis-aconitic anhydride (CAA), and ferriporphyrin. Under the acidic microenvironment of tumors, the CAA hydrolyzes, leading to the self-assembly of Gi-F-CAA into large nanoparticles (Gi-F). This process enhances tumor endocytosis and GPX4 inhibition due to the assembly-enhanced binding (AEB) effect, increasing the reactive oxidative species (ROS) produced by the Fenton reaction. In vitro and in vivo experiments demonstrate that Gi-F-CAA exhibits enhanced cytotoxicity and tumor accumulation, leading to significant tumor growth inhibition in multiple models, including bladder cancer, multidrug-resistant breast cancer, and large renal cell carcinoma. The study also highlights the potential of Gi-F-CAA in addressing drug resistance and treating large tumors, with excellent biocompatibility and no significant toxicological effects. This work provides a promising strategy for overcoming chemoresistance and improving the therapeutic efficacy of ferroptosis-based cancer therapy.