Doubly charged lead monohydrate, [Pb(H2O)](2+), was predicted to be unstable in the gas phase, but it has recently been observed to form in low yield via ligand change between [Pb(CH3CN)](2+) and H2O [Shi, T.; Orlova, G.; Guo, J.; Bohme, D. K.; Hopkinson, A. C.; Siu, K. W. M. J. Am. Chem. Soc. 2004,126,7975-7980]. Here we report that abundant [Pb(H2O)](2+) is formed in the gas phase by ligand-exchange reaction between [Pb(N-2)(n)](2+) (n = 1-3) and water after collisional activation. Density functional theory has been used to examine the ligand-exchange reaction profile. A comparison of the potential-energy surfaces between [Pb(N-2)](2+) and [Pb(CH3CN)](2+) reacting with H2O provides strong evidence that the ligand-exchange reaction of [Pb(N-2)](2+) with H2O to form [Pb(H2O)](2+) is More efficient than that of [Pb(CH3CN)](2+) with H2O.