PVP-Ru amphiphilic microreactors with Ru nanocatalysts have been synthesized by reducing the complex of Ru ions with poly(N-vinyl-2-pyrrolidone) (PVP) in aqueous media. Microscope and TEM images verified the formation of PVP (K90)-Ru-10 microreactor with 100 mu m in length, and Ru nanocatalysts, which were entrapped inside the microreactors, with 1-3 run in diameter, 20-80 nm in length. The Ru nanoparticles could be protected from aggregation by adjusting the average molecular weight of PVP. The obtained PVP-Ru amphiphilic microreactor system showed high activity in the hydrogenation of unsaturated organic compounds in aqueous media. High turnover frequency (TOF) value of 45,000 h(-1) was achieved in hydrogenation of benzene in aqueous media, at 353 K, under 4 MPa hydrogen pressure. All the hydrogenation TOF values of investigated arenes, olefins and carbonyl compounds exceeded 1000 h(-1) . The recovered aqueous phase containing PVP-Ru microreactor could be reused for at least three times without any significant loss in their catalytic activity. (C) 2007 Elsevier B.V. All rights reserved.