A portable automated pipette includes a linear actuator, a flywheel, an optical coupler and a control circuit. The linear actuator has a step motor and is connected to a control circuit. The step motor has a rotor and is connected to a flywheel. The flywheel includes a plurality of apertures formed on an internal surface of the flywheel. An optical coupler is arranged on two opposite sides of the flywheel and is connected to the control circuit. By means of the step motor, the portable automated pipette can monitor the displacement of the threaded rod to accurately control the picking/dispensing volume of liquid. Furthermore, the portable automated pipette can detect whether an aspirator is removed and can alert the user to check whether there is a wrong operation.