Hydrous tin oxide powders were precipitated at room temperature via the neutralization of sodium stannate with gluconic acid, The gluconic acid was generated by the oxidation of glucose, with the assistance of a glucose oxidase/catalase system. The hydrous tin oxide, which had a large surface area, was obtained when a high concentration of enzymes was used as a solution. However, the apparent sizes of the precipitates were similar to 0.3 mu m, independent of the enzyme concentration, The precipitates were converted to tin oxide via calcination at temperatures >400 degrees C.