Disclosed is a fiber reinforced plastic wire used as the overhead transmission cable. The fiber reinforced plastic wire for a strength member of an overhead transmission cable according to the present invention includes a wire having a predetermined diameter and composed of thermoset matrix resin; and a plurality of high strength fibers dispersed parallel to a longitudinal direction in an inside of the wire, the high strength fibers being surface-treated with a coupling agent to improve interfacial adhesion to the matrix resin. The fiber reinforced plastic wire of the present invention has the high tensile strength at the room temperature and the high temperature since its high strength fiber is surface-treated with a coupling agent. The fiber reinforced plastic wire can be also effectively used as the strength member in the overhead transmission cable since it has the excellent low coefficient of thermal expansion, etc. and is light-weight.