The photoluminescence characteristics of zinc oxide films prepared by spray pyrolysis technique were studied as a function of the substrate temperature, film thickness, and post heat treatment. The ZnO films with the (002) plane oriented wurtzite structure were formed in the temperature range 250-350 degrees C and post heat treatment did not affect the crystal structure of the films. It was observed that the intensity of green luminescence that was centered at about 510 nm increased with increasing film thickness. For films with the same thickness, the intensity of green emission decreased with an increase of the value of the O/Zn ratio as determined by X-ray photoelectron spectroscopy. Post heat treatment in a hydrogen atmosphere resulted in a decrease of the value of the O/Zn ratio and an increase of the intensity of green emission.