A cross-linked poly-N-isopropylacrylamide (polyNIPAM) nanocapsule, TH@PC, containing thionine (TH), an organic photosensitizer, has been synthesized. This capsulated polymeric photosensitizer promotes a singlet oxygen oxygenation (O-1(2)) accurately controlled by temperature: it shows high oxygenation activity at low temperature, but shows activity decrease with a rise in temperature, resulting in almost zero activity at >40 degrees C. The clear on-off activity control is driven by a heat-induced structure change of the capsule from the swollen single capsule to contracted state, and then to aggregate. behaving as an intelligent O-1(2) filter. At low temperature, the capsule exists as the swollen single capsule. which allows O-1(2) diffusion to bulk water, resulting in high oxygenation activity. A rise in temperature leads to contraction of the capsule, reducing the mesh size of the capsule wall. This suppresses O-1(2) diffusion to bulk water and shows decreased activity. Intercapsule aggregation at > 30 degrees C further suppresses O-1(2) diffusion and shows almost no activity. The capsule promotes reversible activity control regardless of the heating/Cooling process and can be reused with a simple recovery process.