Resume : The possibility to improve an efficiency of electrostatic harvesters by usage of polymer/nanostructured carbon (PNC) composites was investigated. In electrostatic harvesters the energy of mechanical oscillations is converted into electrical energy through deformation of dielectric layer between plates of charged capacitor. To increase the change of voltage during the deformation of dielectric layer between capacitor plates, its dielectric permittivity should decrease with tensile deformation. As a candidate for such a dielectric material PNC composite was chosen. Capacitor samples containing PNC dielectric layer were elaborated from 1) SVR-3L natural rubber with added curing ingredients (this is used as a matrix); 2) high structure Degussa™ Printex™ EX-2 carbon black with average particle size 30 nm (filler); 3) two brass electrodes (thickness of each electrode 2 mm). Thickness of the PNC composite layer for each sample is 1mm. The concentration of the filler in the composite layer was chosen to be from 2 up to 8 mass parts per 100 mass parts of rubber. Tensile and compressive deformation measurements conducted on PNC samples showed, that under tensile and compressive deformation dielectric permittivity of composite is changing non monotonically. The decrease of the dielectric permittivity with increasing of the tensile and stretching deformation of the dielectric layer was observed. It was also found, that character of dielectric permittivity change for both - tensile and compressive deformation - is different. The change of dielectric properties observed indicates about complex processes taking place in the PNC dielectric layer.