A spectrofluorimetric method has been developed for the determination of terbium(III) based on the formation ofa complex with terephthalic acid [benzene-1,4-dicarboxylic acid (TPA)] in slighdy acidic aqueous solution in the presenceof gelatin. Terbium ion can form a stable complex with TPA with the stoichiometry of 1:2. The best excitation and maxi-mum emission wavelengths are observed at 260 nm and 545 nm, respectively. The fluorescence intensity of terbium com-plex gets the strongest within 20 min and remains stable up to 10 h, and it is proportional to terbium(III) concentration in therange of 4.0×10-5-1.6×10-7 mol·L-1 under the optimum conditions. The fluorescence system has good selectivity, sensitivityand stability. The relative standard deviation is still within ±4% in the presence of 1200-fold amounts of the other lanthanideions when the concentration of terbium(III) is 1.0×10-6 mol·L-1 and common co-existing ions hardly interfere the determi-nation. It has been applied to the direct fiuori A spectrofluorimetric method has been developed for the determination of terbium (III) based on the formation of a complex with terephthalic acid [benzene-1,4-dicarboxylic acid (TPA)] in slighdy acidic aqueous solution in the presence of gelatin. Terbium ion can form a stable complex with TPA with the stoichiometry of 1: 2. The best excitation and maxi-mum emission wavelengths are observed at 260 nm and 545 nm, respectively. The fluorescence intensity of terbium com-plex gets the strongest within 20 min and remains stable up to 10 h, and it is proportional to terbium (III) concentration in therange of 4.0 × 10 -5 -1.6 × 10 -7 mol·L -1 under optimal conditions. The fluorescence system has good selectivity, sensitivity and stability. relative standard deviation is still within ± 4% in the presence of 1200-fold amounts of the other lanthanideions when the concentration of terbium (III) is 1.0 × 10-6 mol·L-1 and common co-existing ions hardly interfere the determi It has been applied t o the direct fiuori