Despite remarkable advancements in cancer immunotherapy, its clinical efficacy remains constrained in solid tumors due to the immunosuppressive tumor microenvironment (TME). Reactive oxygen species (ROS), which exhibit dual regulatory roles in the TME by regulating immunogenic cell death (ICD) and reprogramming immune cell functionality, have emerged as a pivotal therapeutic target. Nano-enabled drug delivery systems present distinct advantages for TME modulation due to their structural versatility, tumor-specific targeting precision, and spatiotemporally controlled drug release. In particular, ROS-responsive nanoplatforms demonstrate multifaceted immunomodulatory potential by synergistically restoring ICD and remodeling immunosuppressive immune cell phenotypes within the TME. These platforms further amplify the therapeutic outcomes of conventional modalities including chemotherapy, radiotherapy, and photodynamic therapy (PDT) through ROS-mediated sensitization mechanisms. This review comprehensively examines recent breakthroughs in ROS-responsive nanosystems for antitumor immunotherapy, emphasizing their mechanistic interplay with TME components and clinical translation potential. Herein, we provide a framework for developing integrated therapeutic strategies to overcome the current limitations in cancer immunotherapy.