An environmentally benign electroless plating process on thermoplastic polymers, which could significantly reduce harmful acids necessary for conventional process, was developed. The process consists of two steps, i.e., supercritical CO2 impregnation and electroless plating reaction in the presence of ethanol and CO2. In the scCO(2) impregnation step, a Pd precursor, which is used as a catalyst for electroless plating reaction, is infused into polymer by taking advantage of solvency and plasticization powers of scCO(2). Then, the polymer containing Pd is immersed in a Ni-P plating solution to conduct the electroless plating reaction. Ethanol and CO2 are added into the solution to enhance solvency of the solution in polymer. A composite layer of Ni-P alloy is formed at the interface between metal and polymer substrate. This provides strong adhesiveness of Ni-P alloy film to the polymer substrates. (C) 2008 Elsevier B.V. All rights reserved.