Abstract We report on the electrical transport measurements of single wall carbon nanotubes (CNs) formed in a single crystal of zeolite (IUPAC Cord AFI) at room temperature. Photo-irradiation effects associated with the resonant photo-excitation of CNs at 900 nm are found in the I– V characteristics. The conductive character changes from ohmic to somewhat semiconducting. The character does not depend on the polarity of the bias voltage. Subtracting the ohmic component, an energy threshold to give nonlinear conduction is found at 0.25 eV. A possibility of the metal–semiconductor junction formation caused by the photo-irradiation is discussed.