Ultrasonic effects on the electroreduction of dimethyl maleate were evaluated systematically by varying the position of the working electrode within acoustic fields produced by different types of ultrasonic devices such as a submersible transducer and a stepped horn. It was found that the electroreduction of dimethyl maleate was greatly affected by the placement of the working electrode in an electrochemical cell. For instance, the diffusion controlled limiting current for the reduction varied periodically along the axis of the ultrasonic beam. and the distance between two maxima or two minima was almost constant, close to the theoretical half wave length in water when the submersible transducer was used as an ultrasonic device, The current efficiency and product selectivity in the preparative scale electroreduction of dimethyl maleate were much higher when the working electrode was placed at the position corresponding to the maxima than that corresponding to the minima. On the other hand. when the stepped horn was used as an ultrasonic device, the limiting current decreased simply with an increase in the distance between the electrode surface and the top of the horn. However. the influence of the placement of the electrode on the preparative electroreduction was quite different from that on the limiting current.