The ZnO films were deposited on quartz glass substrate by RF magnetron sputtering. The ZnO films are highly c-axis oriented with the (002) plane parallel to the substrate. The grains size estimated by the XRD diffraction rises with increase in the Ar/O2 ratio. The optical absorption edge and the near absorption edge characteristics of ZnO films have also been investigated. The optical band gaps of the films have been evaluated from the absorption coefficient of ZnO films. It is found that the value of the optical band gap varys from 3.26 eV to 3.32 eV due to the energy gap enhancement induced by quantum confinement. This variation of band gap can be explained with the theory developed by Brus. For all the films, the absorption coefficient shows the Urbach exponential dependence in the near band edge regime. It is also observed that the value E0 decreases with the Ar/O2 ratio increasing.