ZnO/SiO2 composite films with controlling thickness and vivid structural colors were designed by the electrostatic self-assembly technique from zinc oxide (ZnO) and silica (SiO2) sol particles precursors. The structural color, microstructure and morphology of the films were analyzed using spectrocolorimetry, multi-angle spectrophotometry and scanning electron microscope(SEM). The results showed that the ZnO/SiO2 composite films exhibited higher brightness and chroma compared to the films composed of single components. The color of the composite films varied with the changes of thickness and observation angles. By examining the microstructure and the films thickness varying with the increasing assembly cycles, the film could hardly form a distinct bilayer structure with alternating high and low refractive indices. In fact, it was prone to forming a multilayer microstructure, which had a high refractive layer (H layer), an effective refractive layer (eff layer), and a low refractive layer (L layer). The more vivid and saturated structural colors were probably originated from the multilayer thin film interference.