A novel modified base-catalyzed Sol-Gel process containing polyvinyl alcohol (PVA) has been proposed to prepare the porous SiO film. In this process, the growth of the sol particles was artificially broken off and controlled by acid-stabilising agent and PVA. As a result, a uniform and stable precursor solution was obtained in which the size of sol particles was stable. This new process efficiently overcomes the shortcomings of the traditional base-catalysed Sol-Gel process and can be employed to prepare porous SiO films with desired porosity and thickness. The influence of the catalyst, the reaction temperature, the pH value, the stabilizing agent and the PVA additive on the size of the SiO sol particles is systematically studied in part I.