The solvation structure of Cu+ in water and in liquid ammonia has been investigated using the Metropolis Monte Carlo method. The systems consisting of one Cu+ in 215 solvent molecules have been simulated at a temperature of 240 K for ammonia and 298 K for water, respectively. Cu+-ammonia and Cui-water pair potentials have been newly developed based on ab initio calculations of double-zeta quality. Structural properties were investigated by means of radial distribution functions and their running integration numbers, leading for the first solvation shell to an average coordination number 6 and Cu-N distance of 2.20 Angstrom in ammonia, and to number 6 and Cu-O distance of 2.20 Angstrom in water. The RDFs, coordination number distributions, and pair interaction energy distribution analyses indicate that ligand exchange reactions take place more easily in water than in liquid ammonia.