Photodynamic therapy (PDT) is an effective method for superficial cancer treatment. However, the limited light intensity in tissues, tumor hypoxia, and the low accumulation efficiency of photosensitizers (PSs) in tumors are still major challenges. Herein, we introduce super light-sensitive PS nanoparticles (designated HR NPs) that can increase singlet oxygen (<sup>1</sup> O<sub>2</sub> ) production and improve PS accumulation in tumors. HR NPs have the ability to produce a large amount of <sup>1</sup> O<sub>2</sub> under ultralow power density light (0.05 mW cm<sup>-2</sup> ) irradiation. More significantly, HR NPs have a long circulating time in tumor-bearing mice and can accumulate in tumors with high efficiency. When irradiated by light with a suitable wavelength, the nanoparticles exhibit excellent antitumor efficacy. This work will make it possible to cure solid tumors by PDT by enhancing the therapeutic effects.