Density functional theory calculations were used to study the cooperative activations of the epoxide ringopening hydrolysis catalyzed by the Co-salen complexes. We find that the activation energies of the reactions with two Co-salen catalysts are significantly lower than that of single catalyst. The cooperation effect comes not only from the simultaneous activation of both reactants but also from the cooperative charge transfer during the reactions. The transition states analysis indicates that the preferential reaction pathway is a SN2 reaction, which explains the second order kinetic dependence on the concentration of the catalysts found in the experiments. (C) 2009 Elsevier B. V. All rights reserved.