Undoped and Na-doped ZnO thin films were deposited on Si(1 1 1) substrate by the sol–gel method.Microstructure, surface topography and optical property of the thin films have been investigated. X-ray diffraction analysis showed that all the thin films had a polycrystalline hexagonal wurtzite structure. The 8 at% Na-doped ZnO thin films exhibited high c-axis preferred orientation. Surface topography revealed that average grain size of ZnO thin films annealed at 873 K increased initially,and then decreased with increasing Na concentration, and average grain size of 8 at% Na-doped ZnO thin films increased with increasing annealing temperature. PL spectra showed that all the thin films produced violet and yellow–green emissions in the visible region. In addition, the effects of Na concentration and annealing temperature on microstructure, surface topography and PL spectra are discusse