A new type of fluorescent pH sensor using allylcalcein as the fluorophore is described. The allylcalcein was photo-copolymerized on a silanized glass surface. With increasing pH, the fluorescence intensity decreased noticeably. The proposed pH sensor showed good reproducibility, stability, and response time. In the pH range 6.8-11.7, the fluorescence intensity of membrane varied linearly as a function of pH. It has been applied to the analysis of wastewater, river water, and spring water samples.