We report in this article the use of thermosensitive water-dispersible polymer brush-grafted polymeric particles as carriers for Pd nanoparticles for the catalysis of hydrogenation of styrene in an aqueous/organic biphasic system. Thermoresponsive poly(methoxytri(ethylene glycol) methacrylate) brushes were grown from initiator-functionalized core-shell cross-linked poly(t-butyl acrylate) (PtBA) particles via surface-initiated atom-transfer radical polymerization. The t-butyl group of PtBA in the core was removed with trifluoroacetic acid, followed by loading of Pd2+ cations through ion exchange. Pd nanoparticles were prepared by reduction of Pd2+ ions with ethanol at 70 degrees C. Dynamic light scattering studies showed that the Pd nanoparticle-loaded thermosensitive hairy particles in water began to shrink when the temperature was above 30 degrees C. The supported Pd nanoparticles efficiently catalyzed hydrogenation of styrene in an aqueous/octane biphasic system and were reused five times with no changes in the yields in the first three cycles and slight decreases in the fourth and fifth cycles after the same period of time. Kinetics studies showed that the catalytic activity of Pd nanoparticles was modulated by the phase transition of the thermosensitive brush layer, resulting in a non-Arrhenius dependence of apparent initial rate constant, k(app), on temperature.