The IR laser irradiation of a gaseous mixture of iron pentacarbonyl–methoxytrimethylsilane–ethene in argon induces ethene-photosensitized decomposition of iron pentacarbonyl into elemental iron and decomposition of methyltrimethoxysilane into species that polymerize into methylmethoxysilicone. These two concurrent gas-phase processes allow formation of iron–iron oxide/methylmethoxysilicone nanocomposite. Spectral analyses and electron microscopy reveal the nanocomposite as consisting of iron clusters oxidized in outer layers and covered with the organosilicon polymer. The procedure shows its potential for gas-phase synthesis of iron-based clusters embedded in a polymer matrix. Copyright © 2004 John Wiley & Sons, Ltd.