The synthesis of pH sensitive organic-inorganic polymer hybrids from poly(2-hydroxyethyl methacrylate) derivatives and alkoxysilane is described. To a reaction mixture of poly(2-hydroxyethyl methacrylate) derivatives, tetramethoxysilane, 2',7'-bis(carboxyethyl)-4-or 5-carboxyfluorescein (BCECF) as a fluorescent probe, and ten equivalents of HCl aqueous solution in methyl ethyl ketone/propanol (7/3, v/v) were added. The resulting mixture was kept stirring at room temperature for 1 h and was heated at 40degreesC for 2 weeks. The changes of the pH were estimated as changes in the fluorescence intensity with the pH sensitive fluorescence probe BCECF trapped within the obtained polymer hybrid. Consequently,the pH value was found to be proportionate to the fluorescence intensity.