Hydrogen doping was electrochemically performed on the title coordination polymer, catena-mu-N,N'-bis-(hydroxyethyl)dithiooxamidatocopper(II), (HOC2H4)(2)dtoaCu. From X-ray photoelectron spectroscopy, the oxidation state of Cu(II) in (HOC2H4)(2)dtoaCu was revealed to be reduced to the Cu(I,II) mixed-valence state on hydrogen doping. While the spin susceptibility increases during initial hydrogen doping, it decreases and then shows no temperature dependence as the hydrogen doping proceeds. The temperature-independent behavior is supposed to be derived from Pauli paramagnetism.