The structures and energies of hydrated oxalate clusters, C2O42-(H2O)(n), n = 6-12, are obtained by density functional theory (DFT) calculations and compared to SO42-(H2O)(n). Although the evolution of the cluster structure with size is similar to that of SO42-(H2O)(n), there are a number of important and distinctive futures in C2O42-(H2O)(n), including the separation of the two charges due to the C-C bond in C2O42-, the lower symmetry around C2O42-, and the torsion along the C-C bond, that affect both the structure and the solvation energy. The solvation dynamics for the isomers of C2O42-(H2O)(12) are also examined by DFT based ab initio molecular dynamics.