The structures and properties of phenol and its complex were characterized at the Hartree-Fock (HF), the second-order Moller-Plesset perturbation theory (MP2), and complete active space self-consistent field (CASSCF) levels for the ground state (S-0) and at the configuration interaction with single excitation (CIS) and CASSCF levels for the excited electronic state (S-1). The intermolecular interaction has little influence on the structures of phenol and water. However, a significant change is found in the properties upon complex, and this has been discussed in detail. A comparison with the experimental findings shows that the present calculations provide a good description of the nature of phenol and its complex in S-0 and S-1.