In this work, a novel route to synthesize biomolecule/metal composite nanospheres is proposed. This method combines the advantages that the silver nano-particles and bovine serum albumin (BSA) can be precipitated simultaneously from water-in-oil microemulsion by the easy control Of CO2 pressure, which was revealed by our high-pressure UV-VIS spectra. The Ag/BSA nanocomposites were successfully prepared using this method. The transmission electronic microscopy (TEM) of the obtained nanocomposite shows that the small-sized Ag nanoparticles are immobilized by the BSA nanospheres, and the phase structure was characterized by X-ray diffraction (XRD). The Ag/BSA nanocomposites show absorption properties at a wavelength around 435 nm. (C) 2004 Wiley Periodicals, Inc.