To provide a power transmission belt in which an ethylene--olefin rubber composition adheres to a fiber cord.

In this power transmission belt, a core wire 2 is buried in an adhesive rubber layer 3 along a belt longitudinal direction, a compressed rubber layer 4 is arranged on the side of a transmission surface adjacently to the adhesive rubber layer, and an expansion rubber layer is arranged on the side of a back surface. The adhesive layer consists of the ethylene--olefin rubber composition. The fiber cord forming the core wire is treated with a first treatment liquid consisting of an isocyanate composition or an epoxy composition. Next, the fiber cord is treated with a second treatment liquid consisting of a resorcinol-formalin-rubber latex in which a latex contains at least styrene and vinyl pyridine and the content of the styrene is 30-60 parts by mass to 100 parts by mass of the latex. Further, the fiber cord is treated with a third treatment liquid with a vulcanizing agent added to the ethylene--olefin rubber composition. After that, the fiber cord is subjected to contact-vulcanization with and adheres to an unvulcanized composition of ethylene--olefin rubber.