A simple,rapid and sensitive fluorescence analytical method was developed for the determination of thiamazole based on the quenching of gold nanoparticles in different aggregation states to rhodamine B.The mechanism of the detection system was discussed,and the effects of experimental factors such as pH value,reaction time and concentrations of the involved reagents were investigated.Under the optimum conditions,calibration curve was linear in the range of 4.38×10-8 -0.876×10-5 mol/L with the detection limit of 3.30×10-8 mol/L.The method was successfully applied in the determination of thiamazole in thiamazole tablets.