Growth and structure of picene thin films on SiO2 surface were studied from ultrathin film to thick film regimes (nominal film thickness upto 100 nm) by using X-ray diffraction and atomic force microscopy. We found that from initial film growth picene form crystalline grains with a certain multilayer height, in which their crystalline ab-plane orients parallel to the substrate surface. With increasing the film thickness the number of the grains increases with keeping the grain height until the substrate surface is fully covered. These results indicate that picene films exhibit island growth mode on SiO2 surface.