The effects of hydration on the dimerization energies and structures of acetic acid dimers are studied by the reference interaction site model self-consistent-field (RISM-SCF) method. Comparisons of the RISM-SCF results are also made with those obtained from the self-consistent reaction field (SCRF) methods to examine the dielectric effects of the solvent. The RISM-SCF method predicts the marked stabilization due to solvation in the dimer structures with large dipole moments. From the decomposition analysis of the excess chemical potential, the contribution from the free carbonyl oxygen is found to be much larger than the other atoms for the stabilization of these dimers in aqueous solution. Such a stabilization in the polar dimers is not obtained from the simplest SCRF method that considers only the solute dipole.