A pedal-crank assembly for bicycles includes a pedal configured to be used as a safety lock for the bicycle and a member for fast and easy removal of the pedal from the crank. The pedal-crank further includes a frame rotatably mounted on a pin and a shaft rotatably mounted inside the pin. The pedal has spherical bodies housed inside housing of the shaft. The pin has holes which receive the corresponding spherical bodies. A key lock is mounted to the pedal and configured to be actuated to move the shaft.