The results of the second-order Moller-Plesset perturbation theory calculations with the au-cc-pvTZ basis set for the NH3...H2O complex have been used to parametrize a set of atom-atom potentials. A simple nonpolarized and polarized ammonia-water potential is proposed. The quality of these potentials has been tested by performing the rigid body Diffuse Monte Carlo calculations of the energetics, rotational and quadrupole coupling constants for dimer H2O...NH3. The present potentials are the first ones predicting the structures of the trimers (H2O)(2)...NH3 and (NH3)(2)...H2O confirmed by ab initio calculations. These potentials were successfully used in Monte Carlo simulations of the interaction of ammonia with an ice particle (N. Uras, V.; Buch, J. P.; Devlin, J. Phys. Chem. B 2000, 104, 9203).