The indium-doped ZnO nanofiber thin film has been deposited by spray pyrolysis method. Donor level and barrier height energies for the film were determined from the temperature dependence of the conductivity and were found to be E-D = 0.026 and E-B = 0.55eV, respectively. The conduction mechanism of the indium-doped ZnO nanofiber thin film was shifted from band conduction including ionized impurity scattering to grain boundary scattering. The optical band gap values of the indium-doped ZnO nanofiber thin film at different annealing; temperatures were calculated and were found to be in the range of 3.304-3.245 eV. The direct optical band gap shifted to the lower energy as a consequence of the thermal annealing on film. The Urbach energy of the film was changed with annealing temperature. The refractive index dispersion curve of the film annealed at 500 degrees C obeys the single oscillator model. The E-o and E-d dispersion parameters were found to be 4.132 and 12.605 eV, respectively. (c) 2006 Elsevier B.V. All rights reserved.