In present study, sol gel spin coating method was used to fabricate the nanostructure SnO2 films using the tin(II) acetate solutions. The solutions were spin coated on p-Si substrates and the obtained films was annealed at different temperatures. To investigate the influence of the annealing temperature of n-SnO2 films, the structural and microstructural properties were performed using X-ray diffraction (XRD) and field emission scanning electron microscopy (SEM), respectively. XRD results showed that the average crystallite size of the films was increased with increasing annealing temperature. It is seen that the surface morphology of nanostructure SnO2 films are almost homogeneous and particle size values of the films are approximately 10 nm. In addition, the pn heterojunction diode was fabricated by depositing SnO2 film at 600 degrees C on p-Si substrates. The electrical properties of the n-SnO2/p-Si diode were characterizedby I-V techniques. The ideality factor and barrier height of the diode were calculated. The n value of the heterojunction diode was found to be 5.22. The phi(b) value of the nanostructure SnO2 film was found to be 0.49 eV. It was determined that the interface states played an important role in the conduction mechanism of the diode. The diffuse reflectance spectra of the nanostructure SnO2 films were measured and the optical band gap values were determined using Kubelka-Munk theory.