Abstract: In this work, we have determined the pK_α valuc of 4-nitro-2, 3, 5, 6-tetrafl-uorophenol and studied the relationship between pK_α and the acceleration rales of β-cyclodextrin-catalyzed hydrolysis of subslituled phcnyl esters of trans-fcrrocenc-acrylic acid and ferrocenylcyclopropanccarboxylic acid.It has been found that the acceleration rates are dependent on the electronic nature of the substituents. It obeys Hammett linear free-energy relationship since the phcnyl. groups of subslratcs do not enter but the fcrroccnyl groups enter the cavities of the β-cyclodextrin.