22Porous silicon (PS) prepared from an n-type Si(100) wafer was utilized as a reducing agent and a nanosubstrate for the reduction of rhodium complex ions [RhCl6](3-) from aqueous solution to metallic Rh nanostructures on the surface of the n-type PS. The morphology and the electronic properties of the PS layers as well as the rhodium nanostructures were studied by field emission scanning electron microscopy, X-ray absorption fine structures spectroscopy, and X-ray excited optical luminescence (XEOL). The average particle size of Rh nanostructures on PS was estimated to be similar to7 nm by the X-ray diffraction pattern. The specificity of XEOL allowed for the investigation of the effect of Rh nanostructures on the optical properties of PS.