Carbon monoxide (CO) based gas therapy has been an emerging strategy for cancer treatment. However, the uncontrolled release of CO and limited therapeutic efficacy of monotherapy are two major obstacles for clinical application. To overcome these issues, human serum albumin (HSA) nanoparticles combined with manganese dioxide (MnO₂) were developed to deliver a photosensitizer (IR780) and CO donor (MnCO) for a synergistic therapy combining CO gas therapy and phototherapy. The nanoparticles (HIM-MnO₂) formed catalyze hydrogen peroxide to produce oxygen for hypoxia relief. With laser irradiation, it can increase the generation of reactive oxygen species for the enhancement of photodynamic therapy (PDT). Furthermore, the generated heat of photothermal therapy (PTT) induced by nanoparticles could trigger the release of CO to achieve a therapeutic window for enhanced gas therapy. Due to the co-localization of IR780 in mitochondria, HIM-MnO₂ could accumulate in mitochondria for the synergistic therapy combining CO gas therapy and phototherapy, and could oxidize the mitochondrial membrane and induce more apoptosis. After intravenous injection into tumor bearing mice, HIM-MnO₂ could accumulate at tumor sites and with laser irradiation, tumor growth was significantly inhibited due to the enhanced PDT, PTT, and CO gas therapy. This study provides a strategy with oxygen generating and thermal-responsive CO release to combine phototherapy and CO gas therapy for cancer treatment.