The electronic structures of the ground state and the excited states due to the 3d–3d transition of copper acetate monohydrate are investigated by abinitio calculations. No direct bond is obtained between the two Cu ions, but they are bonded by bridges of the four acetates. The excited states represented by the one-electron excitation of an occupied 3d electron to an unoccupied 3d orbital in either of the two Cu's are located around 1.6-1.8 eV, which corresponds to the energy region of band I. Those of the simultaneous one-electron 3d–3d excitation in both Cu's (i.e., two-electron excitation) are located around 3.2–3.4 eV. They correspond to the energy region of band II. Keywords: copper acetate monohydrate, binuclear compound, bridged bond, 3d → 3d excited states.