We investigated the mechanism of chemical reaction between Bi2O3 glass and water solution during milling. As a result, the frit condition affected discoloration with crystallization. After milling, there was a deposited layer on the frit surface. The layer was composed of leached ions, contaminates of metal oxides, and hydroxides. Bismate glass frit is reacted to the milling solution so that the frit surface is formed with a gel layer. In milling, contaminates contained in milling solution is contributed to the formation of deposed layer on frit surface.