We observed photoreversible switching between weak antiferromagnetic exchange coupling and ferromagnetic exchange coupling in a 2-dimensional cyanide-bridged Cu-Mo bimetallic assembly, [Cu-II(1,4,8,11-tetraazacyclodecane)](2)[Mo-IV(CN)(8)]center dot 10H(2)O. This photomagnetic switching is caused by photoinduced electron transfer from Mo-IV to Cu-II by irradiation with blue light, and photoinduced back electron transfer by irradiation with red light.