The geometric and electronic properties of AumPdn (m+n≤6) binary clusters were investigated at the UBP86/LANL2DZ and UB3LYP/def2-TZVP levels of theory. Structural features, binding energies, vertical ionization potentials, vertical electron affinities, charge transfer, and binding characteristics were determined for each Au-Pd binary cluster. For the five-and six-atom Au-Pd binary clusters, except for the mono-substituted mixed clusters (AunPd and AuPdn, n=5 or 6), the palladium atoms combined to form a Pdcore and the ld atoms were located around the Pdcore to produce the PdcoreAushell structure. The highest occupied molecular orbital (HOMO), the lowest unoccupied molecular orbital (LUMO), vertical ionization potentials (VIP), vertical electron affinities (VEA), Fermi levels, and chemical hardness of the AumPd and AumPd2 clusters are similar to those of the pure ld clusters, indicating an odd-even oscillation. The electronic properties of the mixed clusters, such as the HOMO, LUMO, VIP, VEA, Fermi levels, and chemical hardness, are proportional to the spatial structure and the Au/Pd atomic ratio of the mixed clusters. A very large electronic charge transfer from Pd to Au was found for the binary clusters, indicating a bonding interaction between Au and Pd atoms in the mixed cluster. The electronic properties of the Au-Pd binary clusters reveal that the reactivity of the Au-Pd binary clusters toward small molecules, such as O2, H2, and CO, is higher than that of the pure ld clusters.