The energy relaxation rate of a CN- ion in water at 300 K has been calculated using the centroid molecular dynamics (CMD) simulation method. The simulation consisted of 107 water molecules and a single CN- ion. An independently parameterized three site CN- model was employed along with an ab initio potential for the CN- bond coordinate. A flexible water model designed for quantized bulk water simulations was employed for the solvent. The equilibrium simulation results are seen to give a reasonable structure of the CN- ion and its solvation in water. The calculated relaxation behavior is found to be biexponential with a fastest time scale of about 15 ps, which is comparable to the experimentally observed value.