The fluorescence of vanillin and ethylvanillin in aqueous solution was investigated in the presence of α-, β-, and γ-cyclodextrin (CD). The fluorescence intensity of vanillin was enhanced with increasing CD concentration in the order of γ＜β＜α-CD. Benesi-Hildebrand (BH) plot based on these fluorescence data showed the linear relationship between 1/(I-I_0) and 1/[CD]_0, where I0 and I are the fluorescence intensities in the absence and presence of CD, respectively, and [CD]_0 is initial concentration of CD. The results indicated that 1:1 vanillin-CD inclusion complex was formed under the experimental condition. The binding constants of vanillin against CDs from the BH plot were in the order of α＜γ＜β-CD. The binding constant of vanillin to β-CD was estimated as 2.7×10^2×M^{-1}. The binding constants of ethylvanillin were 4-5 times smaller than those of vanillin. The binding ability of vanillin to β-CD became reduced with increasing the concentration of methanol.
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