The new palladium(II) complex, [Pd(bpy)(AtC3)](2+), where bpy = 2,2'-bipyridine and AtC3 = N-(9-anthracenylmethyl)-1,3-propanediamine, was synthesized and characterized. The crystal structure of [Pd(bpy)(AtC3)](2+) was determined. An intramolecular p-p stacking interaction was observed between anthracene and bipyridine. [Pd(bpy)(AtC3)](2+) exhibited 20S proteasome inhibitory activity. [Pd(bpy)(AtC3)](2+) also inhibited the proteolytic activity of cathepsin B, but not that of a-chymotripsin. Thus, [Pd(bpy)(AtC3)](2+) showed moderate selectivity for proteases. The binding mode of [Pd(bpy)(AtC3)](2+) to 20S proteasome was shown to be irreversible in a washout assay.