The reference interaction site model-self-consistent field (RISM-SCF) method, which has been proposed a while ago to calculate the electronic structure of a solvated molecule, is applied to a classical problem of the acidity of halo-substituted acetic acids in aqueous solution. The well-established experimental result, i.e., the inversion of the-acidity from (fluoroacetic acid > chloroacetic acid) in the gas phase to (fluoroacetic acid < chloroacetic acid) in the aqueous phase is reproduced qualitatively. Detailed analyses are presented with respect to the solvent effect on the electronic structure of solute, the solvent structure around the solute, and the energetics associated with the solvation as well as the substitution.