An optical sensing approach for the detection of saccharides based on reversible boronic acid-diol complexation in a lipophilic polymer membrane is presented. The complexation of saccharides with phenyl boronic acids that are immobilized in a hydrophobic polymer matrix produces a stable boronate anion and liberates a mobile hydrogen ion. The change in fluorescence intensity of the sensing films resulting from the increase in hydrogen ion concentration is thus directly related to the ambient saccharide concentration. By monitoring the pH change in a bulk optical film, we were able to detect D-glucose, D-fructose, D-galactose, and D-sorbitol with a concentration range from 0.1 to 100 mM at physiological pH 7.4.