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Nanocrystalline ZnO thin films were grown by pulsed laser deposition technique on polycor substrates. The operation laser fluence of 2.0 J·cm-2 and film thickness of 60 nm were fixed while varying target-to-substrate distance (20-135 mm), substrate temperature (100-500 °C) and annealing temperature (300-700 °C). Structural and morphological investigations carried out by reflection high-energy electron diffraction, scanning electron and atomic force microcopies, have shown a strong influence of deposition technique parameters on grain size of the zinc oxide films. Atomic force microscopy showed the surface roughness decreasing and grain size increasing with the annealing treatment of the as-deposited films. The resistivity and Hall mobility of ZnO films were increased with substrate temperature and/or annealing temperature rise. The gas sensing characteristics of the films were investigated towards nitrogen dioxide and ammonia at a selected operating temperature (22 and 50 °C).