Pulsed laser deposition (PLD) technique is used to deposit undoped ZnO thin films at different substrate temperatures on glass substrates. XRD and atomic force microscopy (AFM) studies indicated that the obtained ZnO thin films were hexagonal wurtzite type structure with strong (002) c-axis orientation. The resistivity decreased rapidly with the increase of substrate temperature to a minimum of 1.74×10^(-3) Ω-cm at 150℃, and then increased. The band gap energy, measured from reflectance spectra, lies between 3.2 and 3.3 eV. There is an absorption edge blue shift with decreasing the substrate temperature. This shift obeys an inverse relation with the average crystallite size, typical of quantum confinement effect in very small nanoparticles.