The composite poly(2-vinylpyridine) (P2VP)-Ag(+) foam-like thin films were prepared at the interface between AgNO(3) aqueous solution and polymer chloroform solution at 25 degrees C. An X-ray photoelectron spectroscopy (XPS) investigation indicated that Ag(+) ions in the composite films were partially transformed to Ag atoms after irradiated by UV-light and completely transformed to Ag atoms after being treated with KBH(4) aqueous solution. Ag nanoparticles with the average sizes of 2.71 +/- 0.82 and 3.28 +/- 1.20 nm were generated in these two transferred films with different treatments, respectively. Transmission electron microscopy (TEM) and high-resolution TEM (HRTEM) images showed clearly that the composite films were composed of microcapsules whose walls had multilayer structures, and the nanoparticles were incorporated in the walls. The formation of the composite films at the liquid-liquid interface was attributed to the adsorption of the polymer molecules at the interface, coordination between the pyridine groups and Ag(+) ions, and self-assembly of the composite molecules. Furthermore, the catalytic activity of the composite films was evaluated using the reduction of 4-nitrophenol (4-NP) by KBH(4). The results demonstrated that the composite thin films have high and durable catalytic activity.