Much research has been directed toward the development of electrically switchable optical materials for applications in memory and display devices. Here we present experimental evidence for an electric-field-induced charge-transfer phase transition in two cyanometalate complexes: Rb(0.8)Mn[Fe(CN)(6)](0.93).1.62H(2)O and Co(3)[W(CN)(8)](2)(pyrimidine)(4).6H(2)O, involving changes in their magnetic, optical, and electronic properties as well. Application of an electric field above a threshold value and within the thermal hysteresis region leads to a transition from the high- to the low-temperature phase in these compounds. A model is proposed to explain the main observations on the basis of a para-ferroelectric transition. Our observations suggest that this new concept of electrical switching, based on materials exhibiting charge-transfer phase transitions with large thermal hysteresis loops, may open up doors for novel electro-optical devices.