Por-Si surface studies were carried out by Auger electron spectroscopy (AES), thermostimulated exoelectron emission (TSEE), photoluminescence (PL) in visible region and ellipsometry. The spectra of visible luminescence, dependences of refractive index of surface layers on porosity were investigated. The AES and TSEE have been applied for studies of por-Si surface. The elemental composition and thickness of thin films of natural oxide and created in the result of electrochemical etching and further contact with gaseous phase por-Si were analyzed by quantitative AES. Effective thickness of Si y O x C 1 - x - y thin film coatings and their composition after different electrochemical etching regimes and, consequently, por-Si porosity have been evaluated. The Si y O x C 1 - x - y coatings thickness raise with increasing of por-Si porosity. The dielectric amorphous thin films oxygen-carbon coatings might play a significant role in PL of por-Si.