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;: Rb0 8Mn[Fe(CN)(6)](0 93)center dot 1.62H(2)O and Co-3[W(CN)(8)](2)(pyrimidine)(4)center dot 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-erroelectric 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 doom for novel electro-optical devices.