This article reports on the fabrication of hybrid titanium dioxide (TiO₂) nanoparticles grafted with thermoresponsive poly(N-isopropylacrylamide) (PNIPAM) and their self-flocculation effect caused by the thermal phase transition and entanglement behavior of PNIPAM. Surface-initiated atom transfer radical polymerization (ATRP) of N-isopropylacrylamide (NIPAM) was conducted rapidly (within a few minutes) in aqueous solution at ambient temperature by using CuBr/N,N,N′,N′′,N′′-pentamethyldiethylenetriamine (PMDETA) as the catalysts and started from the surface of TiO₂ nanoparticles derivatized with ATRP initiators. Without purifying the inhibitor, the grafted PNIPAM gives low molecular weights (M_n < 3000) and a narrow molecular weight distribution (PDI < 1.1) determined by GPC detection, which gives the hybrid TiO₂–PNIPAM both a self-flocculation effect with rapid response to temperature, and a temperature-controlled switching effect of the degradation of Rhodamine B in solution. Moreover, the hybrid TiO₂–PNIPAM exhibits a particular dispersion effect at ambient temperature in aqueous solution caused by the hydrophilicity and the entanglement interaction of the grafted PNIPAM. These effects for hybrid TiO₂–PNIPAM provide a new way to re-use TiO₂ nanoparticles for pollutant degradation systems and to avoid secondary pollution effectively due to the thermal phase transition and entanglement behavior.