Reflective second harmonic generation (RSHG) is used to analyze the growth condition of poly crystal zinc oxide (ZnO) film with a c-axis orientation, grown on the Si substrate by RF magnetron sputtering technique. It elucidates physical phenomena exhibited by growing ZnO thin films. Connecting with analytical results of the characteristic parameters derived from the X-ray patterns and SEM images, the relationship between the RSHG intensity and the substrate temperature reveals that the effect of the grain boundaries is the domination of the RSHG mechanism. The inclined structures of ZnO films on the Si substrate are explained with reference to these RSHG patterns. (c) 2006 Elsevier B.V. All rights reserved.