The cooperative enhancement of water binding to the antiparallel β-sheet models has been studied by quantum chemical calculations at the MP2/6-311++G**//MP2/6-31G* level. The binding energies of the two antiparallel β-sheet models consisting of two strands of diglypeptide are calculated by supermolecular approach. Then water molecules are gradually bonded to the diglypeptide by NH···OH2 and CO···HOH hydrogen bonds. Our calculation results indicated that the hydrogen bond length and the atom charge distribution are affected by the addition of H2O molecules. The binding energy of antiparallel diglypeptide β-sheet models has a great improvement by the increasing of the hydrogen bond cooperativity and the more H2O molecules added the more cooperativity enhancement can be found. The orbital interactions are calculated by natural bond orbital analysis, and the results indicate that the cooperative enhancement is closely related to the orbital interaction. © 2012 Wiley Periodicals, Inc.