A reagent tablet for determination of fluoride ion has been prepared using ethylenediamine-N,N,N',N'-tetraacetate complex of zirconium (Zr-EDTA), 3-hydroxy-2'-flavone (FS) and an appropriate pH buffer. Dissolving of the tablet into water exhibits an intense blue fluorescence (lambda(max)=460 nm) upon excitation at 377 nm and the fluorescence intensity decreases with the presence of fluoride ion. Hence, a simple fluorescent detection procedure for fluoride ion in aqueous media was successfully constructed with this tablet. The principle of this detection system is the ligand exchange reaction of FS bound to Zr-EDTA with fluoride ion. The present system provides an easy, rapid and selective determination method of fluoride ion ranging from 5 x 10(-6) to 1 x 10(-3)mol dm(-3). The measurement of real samples with this tablet showed the similar results as those by the common method with the Alfusone reagent.