A thermoregulated biphasic system composed of n-heptane and poly(ethylene glycol) (PEG) monoalkyl ether, which underwent a reversible change from biphase to monophase regulated by temperature, was reported and used for PETPP/Ru (PETPP=P-[p-C6H4O(CH2CH2O),,H](3), 3n = 14) complex catalyzed hydrogenation. Under the optimal reaction conditions: T= 80 degrees C, time = 3 h, P = 5 MPa, the yield of n-octane reached up to 100% and the TOF was 332 h(-1). After reaction, on cooling to room temperature, the catalyst-containing poly(ethylene glycol) monoalkyl ether phase could be easily separated from the product-containing n-heptane phase by simple decantation and reused directly for the next run. Catalytic activity remained almost the same within ten successive runs. Analysis of ICP-AES demonstrated that Ru leaching to the n-heptane phase was under the detection limit of the instrument in this thermoregulated biphasic system. (c) 2006 Elsevier B.V. All rights reserved.