Concrete fine powder that is residue after aggregates recycling of demolished concrete and acid water that is used for acid cleaning of rusted steel plates are the wastes thrown away as valueless substances. However, there is possibility for obtaining some valuable materials from the two wastes by applying chemical reaction between them, because the former is alkaline substance and the latter is acid solution. In this paper, the production process of obtaining valuable materials from the wastes was developed. Silica and calcium carbonate of more than 95% in purity could be successfully obtained through the developed process.