The gravity drainage of foam leads to the deformation of liquid film that results in the surface tension gradients and the heterogencity of film thicknesses. The deformation of liquid films causes the rupture of films. However, the deformation of liquid films produced from surface active agents solution can be spontaneously restored by the "Maran ni effect". This ability of restoration is connected with the surface rheology. The aim of this paper is to investigate the surface rheology of foaming agent C12E8 by the (lamped longitudinal waves method and explains the restoration mechanism of surface tension gradient due to the stretched surface. It is shown that the surface of foammg agent C12E8 is viscoclastic and that the surface dilational modulus depends on the frequency of the perturbation. The increase of dilational modulus with concentrations at lower concentration is caused by the surface adsorption of molecules C12E8, while the decrease at higher concentration is caused by bluk to surface diffusion exchange.