Abstract: Isoniazid (INH) drug tablets were ground, and the drug powder containing 2.00 mg of INH was taken. After adding 20 mL of water, the mixture was stirred for 2 min with glass rod. The obtained solution was diluted to 100.0 mL by water. An aliquot (5.00 mL) was taken, and centrifuged for 2 min, and 1.00 mL of the supernatant was taken, and diluted to 10.0 mL by water to prepare the INH sample solution. Then 1.00 mL of 0.20 mol·L^-1 acetic acid-sodium acetate buffer solution (pH 4.6), 1.50 mL of 0.50 g·L^-1 NaB(C₆H₅)₄ solution, and 2.00 mL of 1.00 g·L^-1 CuSO₄ solution were added and mixed, and 1.00 mL of INH sample solution was added. The mixture was diluted to 10.0 mL by water, shaken for 0.5 min, and settled to react for 10 min. INH reduced Cu(Ⅱ) to Cu(Ⅰ), and Cu(Ⅰ) reacted with B(C₆H₅)₄^- to form CuB(C₆H₅)₄ complex, which further aggregated to form associated particles, forming a solid-liquid interface with strong resonance light scattering signal. An appropriate amount of the above solution was taken and placed into a fluorescence spectrophotometer, and synchronously scan was made on excitation (λ_ex) and emission (λ_em) wavelengths in the range of 200-700 nm (λ_ex=λ_em), reading the signal intensity I_RSS of the resonance scattering peak at 397 nm. The reagent blank was analyzed simultaneously to obtain I⁰_RSS, with ΔI_RSS (ΔI_RSS=I_RSS-I⁰_RSS) for quantification. It was shown that 100 times starch, 120 times glucose, 150 times maltose, 200 times sucrose, 600 times NO₃^-, 800 times Cl^-, 1 000 times K⁺, and 800 times Zn²⁺ did not interfere with the determination of INH. Linear relationship between values of the mass concentration of INH and ΔI_RSS of the reaction system was kept in the range of 0.010-2.00 mg·L^-1, with detection limit (3s/k) of 0.004 mg·L^-1. The proposed method was used for the analysis of actual samples, and RSDs (n=5) of the INH determined values were found in the range of 1.8%-2.6%. The determined values were basically consistent with those obtained from the high performance liquid chromatography in the Pharmacopoeia of the People's Republic of China (2020 version). Test for recovery was conducted according to the standard addition method, giving recoveries in the range of 97.0%-99.0%.