Abstract: Characteristic fluorescence produced by rhodamine B was observed with its excitation and emission wavelength at 554 nm and 575 nm respectively.Rhodamine B was oxidized rapidly by the ·OH free radical produced by the reaction between Mn2+ and hydrogen peroxide in a weakly alkaline solution,leading to the quenching of fluorescence,on the other hand,behavior of partial elimination of the free radical (·OH) was shown by the reaction with water-extracts of some Chinese herbal medicines.And when the water extract of certain Chinese harbal medicine was added to the fluorescence quenching reaction system mentioned above,a decrease of magnitude of the quenching of fluorescence intensity was found.Based on these facts,a method of synchronous fluorospectrophotometry (Δλ=21 nm) was proposed for the determination of rate of elimination of (·OH) free radical by extracts of Chinese herbal medicines.The rate of elimination of (·OH) free radical,or in another expression,the anti-oxidation activity of 11 Chinese herbal medicines were determined,and as shown by the experimental results,the gallnut showed strongest anti-oxidation activity among the 11 medicines tested.