The effects of solvent and pressure on the rate of the base-catalyzed decomposition of diacetone alcohol have been measured in two aqueous mixtures involving methanol and isopropanol at 20.00～40.00℃, and in aqueous methanol at 30.00℃, respectively. The constant-pressure activation parameters for the decomposition in various compositions of solvent exhibit that ΔG_P≠ is slightly dependent on the solvent composition but oppositely in the direction due to the solvent system, whereas ΔH_P≠ and ΔS_P≒ in both systems increase in a compensating manner as the content of alcohol rises, having no minima. The activation volume obtained in the methanol system increases also simply without any minimum against the solvent axis. These results are discussed in comparison with those of the ethanol system studied previously
