An improved structure of a transmission structure for an electrically operated bicycle, structured to include an electric mechanism and a pedal coaxially disposed on a pedal shaft of a bicycle. The present invention is characterized in that: a rotating shaft of the electric mechanism is a hollow tube that passes through two sides of the electric mechanism; the pedal shaft of the pedal mechanism penetrates and is disposed within the rotating shaft and is able to rotate therein; and the driving chain wheel is pivotal disposed on an outer side of the rotating shaft. One side of the driving chain wheel is coupled to the rotating shaft of the electric mechanism by means of a clutch, and the other side of the driving chain wheel is coupled to a pedal crank of the pedal mechanism by means of a unilateral bearing.