Photoinduced magnetization was observed in a Prussian blue analog, K0.2Co1-4[Fe(CN)(6)]. 6.9H(2)O. An increase in the critical temperature from 16 to 19 kelvin was observed as a result of red light illumination, Moreover, the magnetization in the ferrimagnetic region below 16 kelvin was substantially increased after illumination and could be restored almost to its original level by thermal treatment, These effects are thought to be caused by an internal photochemical redox reaction, Furthermore, blue light illumination could be used to partly remove the enhancement of the magnetization. Such control over magnetic properties by optical stimuli may have application in magneto-optical devices.