Ab initio quantum chemical calculations were performed on the formamide‐formamidine acid system in the gas phase and in water solution. The solvent effects were modeled by explicit inclusion of three water molecules, which creates the first hydration shell around the solute. Full geometry optimizations without any constraints of these complexes were carried out at the MP2/6-31G(d,p) and MP2/6-31+G(d) levels of theory. Single point calculations were also performed at up to MP4/6-311++G(3df,2p)//MP2/6-31+G(d) computational level to obtain more accurate energies. The role of the basis set and the electron correlation effects on the energy barrier of tautomerization and energy difference between tautomers are analyzed. The minimum energy path (at MP2/6-31+G(d) level) for water-assisted proton transfer in tri-hydrated formamide was followed.