A single crystal of (Cs2Cu7II)-Cu-I[Mo-IV(CN)(8)](4)• 6H(2)O was electrochemically prepared on a Pt wire electrode with a constant potential of +500 mV vs Ag/AgCl electrode. X-ray single-crystal structural analysis showed that this compound consists of a three-dimensional cyano-bridged Cu-Mo bimetallic assembly with a tetragonal structure of 14/mmm. The coordination geometry of Mo-IV is bicapped trigonal prism, and that of Cu-II is five-coordinate of square pyramidal or four-coordinate of square planar. This compound was also prepared as a 0.2-3.0 μ m thick film on a SnO2-coated glass in the same electrochemical manner. When the sample, which shows paramagnetism due to Cu-II (S = (1)/(2)), was irradiated with 450-500 nm light at 5 K, spontaneous magnetization with a Curie temperature of 23 K was observed. This photoinduced change was recovered by a thermal treatment. In the infrared (IR) and electron spin resonance (ESR) spectra after light irradiation, variations in the stretching IR peak of CN bridged to Mo-IV and the paramagnetic ESR peak of Cu-II were observed, respectively. The data indicate that this photomagnetism is caused by the electron transfer from Mo-IV to Cu-II and the ferromagnetic ordering between Cu-II (S = (1)/(2)) and Mo-V (S = (1)/(2)).