[en] 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 discussed.