Abstract: An appropriate amount of isoniazid sample solution and 0.60 mL of 5.00×10^-4mol·L^-1 ferric chloride solution were added into a 10 mL colorimetric tube. The tube was heating by microwave for 2 min, and cooled to room temperature. Then 1.00 mL of 5.00×10^-3mol·L^-1 potassium iodide solution was added and mixed well, 0.30 mL of 1.00×10^-4mol·L^-1 cetyltrimethylammonium bromide solution was added and mixed well. After the mixed solution was diluted to 10 mL with water, and allowed to stand for 20 min, the scattering intensity (I) of the solution was measured at both the excitation wavelength and the emission wavelength of 275 nm, using a fluorescence spectrophotometer. The scattering intensity (I₀) of the blank solution was measured, and ΔI=I₀-I was calculated. Linear relationship was found between ΔI and mass concentration of isoniazid in the range of 0.050-0.25 mg·L^-1, with detection limit (3s/k) of 0.015 mg·L^-1. The proposed method was applied to analysis of isoniazid tablets, giving measured values consistent with the labeled values, and RSDs (n=6) less than 2.0%.