A simple, rapid, sensitive, and low-cost spectrofluorometric method was developed for the determination of Au(III) using 5-(2,3-dimethoxyphenyl)-3-(4-methoxyphenyl)-1-phenyl-4,5-dihydro-1H-pyrazole (L) in ethanol/water. The method is based on the change in the fluorescence intensity at 464 nm after excitation at 355 nm as a result of the reaction between the ligand and Au(III). The fluorescent emission of ligand at 464 nm decreased with the increasing of Au(III) concentration. The ligand concentration, pH effect, response time, and effect of foreign ions were determined. From the results of fluorescence titration experiments, it was found that the ligand (1 x 10 (-7) M) was selective and sensitive to Au(III) in EtOH-H2O (1:1, v/v, phthalate buffer, pH 4.0). The calibration curve showed good linearity in the concentration range of 17.4-237.6 mu g L-1 Au(III). The limits of detection and quantification were 5.2 and 17.4 mu gL(-1) Au(III) with a response time of 1 mm, respectively. Satisfactory accuracy was obtained for standard reference material (CRM-SA-C Sandy Soil C). The proposed method was successfully applied to the determination of Au(III) in tap water, sea water, and stream water samples, and high levels of recovery were obtained.