A pedal assembly includes a pedal, a base and two frames, a chain is connected between the front end of the pedal and a locking member on the shaft of the base. The rear end of the pedal is pivotably connected to the heel plate so that the pedal is pivotable along the stepping direction. The heel plate and the base are positioned by the respective frames which are fixed to the base and the heel plate by screws. By using the screws, the pedal assembly is stable and made at less material. The frames can be adjusted back and forth to meet different users' needs such that the different sizes of the feet of the users can operate the pedal assembly efficiently.