Optimal structures, interaction energies, and harmonic vibrational frequencies of the (H2O)(2)CO ternary complex have been determined from the supermolecular calculations with the aug-cc-pVDZ and the aug-cc-pVTZ basis sets. Energetic properties of the complex have been calculated at MP4 and CCSD(T) levels. We located three low-energy configurations on the potential energy surface corresponding to two isomeric H-bonded cyclic complexes and one linear structure. The tunneling motion of the water molecule across the plane of the heavy atoms ring was studied. The calculations of the vibrational frequencies and infrared intensities for this complex are presented to facilitate the frequency assignments of future experimental spectra.