The effects of the oxygen partial pressure, substrate temperature and laser wavelength on the structural and optical properties of thin films of ZnO grown on silicon and glass substrates by pulsed laser deposition have been studied. Regardless of thickness, all the grown layers are c-axis oriented and optically transparent. At substrate temperatures as low as 300°C, featureless layers with a FWHM value for the (002) XRD reflection less than 0.18° and exhibiting an optical transmission higher than 80% in the visible region were produced. For otherwise identical deposition conditions, the KrF excimer laser (at 248 nm) was always found to produce better quality thin films than the frequency-doubled Nd: YAG laser (532 nm). This is explained by the large difference between the optical absorption coefficients of ZnO at the two wavelengths employed, which play a keu role in the laser-target interaction. SEM investigation of the target surface after deposition revealed very different surface morphologies for the two wavelengths employed supporting this assumption.