It is known that polymer/carbon nanotube composites are being tested for their potential use in optoelectronic devices. It is also known that polyisoprene/nanostructured carbon (PNC) composites have a pronounced resistance change under the influence of mechanical strain and vapour of volatile organic compounds. The goal of this study was to test PNC composites for their potential use as optoelectronic materials. Measurements of relative resistance change of poly- isoprene/nanostructured carbon black composites irradiated by semiconductor laser beam were conducted. One illustration of composites photoresistivity measurements at different intensities of laser radiation is given in Fig.1. Two competing mechanisms of composites resistivity change, induced by laser radiation, have been proposed: 1) photoconductivity of carbon nanostructures and 2) exponential reduction of tunnelling currents between carbon nanostructures in composite caused by to thermo-optically induced matrix expansion. Further photoresistivity and optical studies of PNC composites are in progress.