Siloxane compounds are interesting objects to study due to their properties and a variety of possible functional groups which could be attached to silicon atoms. The octahedron (or cube) oligomeric octasilsesquioxane [RSiO1,5]8 (ОSS) are the most widely used their unique chemical structure and physical property. OSS molecule consists of a rigid crystalline core (SiO1,5)8 of a cubic shape with a diameter of ~ 0.54 nm, bearing eight peripheral group R. Study of the electronic structure octavinylsilsesquioxane was performed by X-ray photoelectron spectroscopy using ultra-high vacuum photoelectron spectrometer firm Omicron (Germany) with a hemispherical electrostatic analyzer (radius of curvature of 125 mm). Experimental results were interpreted with calculations performed by Firefly 7.1G[1] program at density functional theory (DFT) level of approximate employing B3LYP hybrid functional and 6311 (for O, C, H), 6311 ++ (for Si) basis set.figureFig.1 The structure of a moleculeFig.2 Spectrum of the valence regionSeveral various position of vinyl groups were calculated with respect to silicon-oxygen core. The influence of the position of vinyl groups on the total energy, the effective charges and the energies molecular orbital of octavinylsilsesquioxane was evaluated.