A new Schiff-base ligand with a tripodal structure, N,N′,N″-tri(3-indolemethanal)triaminotriethylamine (TTAIM), was synthesized. Its fluorescence intensity with terbium(III) was increased by about two orders of magnitude in the present of sodium acetate (NaAc). After the adding of the organic solvent dimethyl sulfoxide (DMSO) to the above system, leading to Tb³⁺ the fluorescence was further enhanced by about 16 fold. The spectrofluorimetric determination of a trace amount of Tb³⁺ based on this phenomenon was carried out. The excitation and emission wavelengths were 330 nm and 545 nm, respectively. Under the optimal conditions, the fluorescence intensities varied linearly with the concentration of Tb³⁺ in the range of 5.7 × 10^-11 -6.3 × 10^-6 mol L^-1 with a detection limit of 5.0 × 10^-11 mol L^-1. The interferences of some rare earth metals and other inorganic ions were described. The method is a selective, sensitive, rapid and simple analytical procedure for the determination of terbium(III) in a high-purity yttrium oxide and synthetic sample. The mechanism for the fluorescence enhancement was also studied.