Infrared spectroscopic ellipsometry (IRSE) was applied for characterization of porous silicon (PSi) electrochemically prepared in acidic fluoride solution. When no formation Of SiO2 was involved in the preparation, an anisotropic distribution of PSi bonds with the terminating molecules was achieved. On the contrary, oxidation of PSi samples during the preparation led to an isotropic structure. IR spectra obtained from organically functionalized PSi surfaces suggested that the morphology of the organic layer on PSi was anisotropic for electrochemical grafting of methyl but not nitrobenzene. Comparison between the IRSE spectra obtained from PSi and Si(I 11) surfaces and application of optical models supported these observations.