This article is a report about the novel fluorescence temperature sensor based on a surfactant-free Poly (vinly alcohol)/borax/2-naphthol hydrogel system. The well-known fluorescence indicator, 2-naphthol, exhibits a change of fluorescence intensity when it is embedded in aqueous PVA/borax gel networks at various temperatures. The blue color emission intensity(PL:lambda(max) = 426 nm) of 2-naphthol in a basic hydrogel changed gradually to strong from 30degreesC to 80degreesC when excitation wavelength was 365 rim. The pH change in the hydrogel system was in the range 0 from 8.50 at 30degreesC to 9.35 at 80degreesC with rising temperature. In the case of salicylic acid, the blue color emission intensity in the acidic gel decreases with rising temperature when excitation wavelength was 365 nm in all cases. The pH change in the hydrogel system was from 2.80 at 30degreesC to 2.40 at 80degreesC with rising temperature. (C) 2004 Wiley Periodicals, Inc.