This study developed a novel biodegradable nanosuspension for localized treatment of postoperative recurrence and brain metastasis of breast cancer. We designed hollow mesoporous organosilica nanoparticles (HMON) coated with iron metal-organic frameworks (Fe-MOF), which have tumor microenvironment dual-responsive degradability and successfully encapsulated the chemotherapeutic drug doxorubicin (DOX). This nanosuspension can not only maintain the sustained release of the drug at the postoperative residual tumor sites but also enhance the intracellular oxidative stress of tumors, significantly promoting tumor ferroptosis. Moreover, the nanosuspension acts as an immune amplifier, stimulating dendritic cells (DC) to secrete chemokines for T cell recruitment and increasing antigen exposure in lymph nodes, thereby significantly activating anti-tumor immune responses in both in-situ tumors and metastatic encephaloma. Especially when used in conjunction with clinical PD-1 antibody, the locally administered nanosuspension can significantly inhibit postoperative recurrence and metastasis of breast cancer. Furthermore, the nanosuspension can be completely biodegraded after local administration, offering good biosafety and promising a new nanotherapeutic strategy for the treatment of breast cancer after surgery. The work was mainly accomplished by doctoral student Min Qian.