Gold nanoparticles (Au NPs) were directly deposited on commercially available poly(methyl methacrylate) (PMMA) beads by the deposition reduction method by adding dropwise of NaBH4 into the aqueous solution of Au(en)(2)Cl-3. The average diameter of Au NPs was 6.9 nm and, in contrast to the case of rapid addition, there were no aggregated particles larger than 20 nm. Catalytic activity of Au/PMMA was tested for the reduction of 4-nitrophenol to 4-aminophenol with an excess amount of NaBH4. Gold NPs on PMMA showed the highest catalytic activity among polymer supported Au NPs previously reported. The reaction rate is the pseudo-first-order with respect to 4-nitrophenol. The pseudo-first-order rate constant and the activation energy were estimated to be 7.2-7.9 x 10(-3) s(-1) at 295 K and 38 kJ mol(-1), respectively. (C) 2008 Elsevier B.V. All rights reserved.