Second-order rate constants (kOH-) have been measured spectrophotometrically for alkaline hydrolysis of Y-substituted phenyl phenyl carbonates (2a-j) and compared with the kOH-values reported previously for the corresponding reactions of Y-substituted phenyl benzoates (1a-j). Carbonates 2a-j are 8 ~ 16 times more reactive than benzoates 1a-j. The Hammett plots correlated with σ -and σ o constants exhibit many scattered points, while the Yukawa-Tsuno plot results in excellent linear correlation with ρ = 1.21 and r = 0.33. Thus, the reaction has been concluded to proceed through a concerted mechanism in which expulsion of the leaving group is advanced only a little. However, one cannot exclude a possibility that the current reaction proceeds through a forced concerted mechanism with a highly unstable intermediate.