A simple and highly sensitive method for the determination of Gemifloxacin Mesylate in bulk drug and pharmaceutical formulations. The method is based on the reaction of Gemifloxacin Mesylate with Tb 3+ in the presence of hexamine at pH 7.2. The fluorescence was measured at 545 nm after excitation at 271 nm. The calibration graph was linear over the range 0.05-1.3 µg mL, with minimum quantification limit (LOQ) of 0.024 µg mL and minimum limit of detection (LOD) of 7.65×10 -3 µg mL. The proposed method was successfully applied for the determination of this drug in its dosage forms.