A simple and highly sensitive fluorometric method is proposed for the determination of H 2 O 2 in milk samples. In this method, non-fluorescent coumarin is oxidised to highly fluorescent 7-hydroxycoumarin by hydroxyl radicals (OH) generated in a Fenton reaction, and the oxidation product has strong fluorescence with a maximum intensity at 456nm and can be used as a fluorescence probe for H 2 O 2 . Under the optimal conditions (2.5×10 −4 mol L −1 iron(II) ions, 4.0×10 −4 mol L −1 coumarin, solution pH 3.0, reaction time 9min, and excitation at 346nm), the proposed method presents wide linear responses between the fluorescence intensity and H 2 O 2 concentration in a wide range from 2.0×10 −8 to 2.0×10 −5 mol L −1 , with a detection limit (S/N=3) of 5.0×10 −9 mol L −1 . After possible interferences are evaluated for a series of chemical substances, the present method has been applied to the determination of hydrogen peroxide in milk with satisfactory results.