The humidity sensor used utilized a fluorescent dye entrapped within a poly(ethylene oxide) or poly(acrylic acid) matrix. The fluorescence intensity increased strongly and linearly with increasing humidity. The wavelength of the fluorescence maximum was 525 nm for the composite with poly(acrylic acid) over the whole range of the humidity. For the poly(ethylene oxide) composite, the fluorescence maximum in the lower humidity region was about 550 nm and it shifted to lower wavelengths with an increase in humidity. In both cases, the intensity of the fluorescence increased linearly with humidity. The 90% response and recovery time for humidity changes was less than 20 s for the poly(ethylene oxide) composite, while a longer time was observed for the poly(acrylic acid) composite.