Conventional pack boriding (CPB) has shortcomings of high processing temperature and long process duration for producing boride coating with an effective thickness. Alternating current field enhanced pack boriding (ACFEPB) is a new approach for overcoming those shortcomings in CPB. In the present work, ACFEPB was carried out on a 45 medium carbon steel at low and medium temperatures (450~800 ℃) by applying a 50 Hz alternating current field (ACF) during the pack boriding for revealing effects of ACF on the treatment. Understanding characterization of the ACFEPB better will lay a good foundation for investigating the mechanism of the ACF on the boriding and optimizing the new process. Experimental results showed that nearly same thick boride coatings were obtained in target surface of samples located in different positions right between the parallel ACF electrodes, while less thick boride coatings were found in samples not within the region. All ACFEPB samples' boride coatings were thicker than that of corresponding CPB, which demonstrated that applying an appropriate ACF could notably enhance the boriding. A linear relation was shown in the profile of ACFEPB coating thickness vs the boriding temperature. The coating thickness of the ACFEPB at 800 ℃ increased with the increase of the ACF current. And the coating thickness vs the boriding time exhibited a parabolic character. Morphology similar to the CPB coating was presented in the ACFEPB coating. The saw-tooth shaped boride penetrated perpendicularly to the substrate. However, fewer or no FeB phase was found in ACFEPB coating when comparing with CPB coating treated at same temperature with same duration. More micro-porosities were found in the near surface zone of single Fe₂B phase coating by ACFEPB, which was an indication that more vacancies moved from the substrate to the near surface region. Although a temperature rise caused by the ACF was detected in the sample during the boriding, the heating effect of the ACF to the sample and the boriding media was not the main reason for ACF's enhancing effect to boriding. The ACF’s electro-magnetic effect should be the main factor for the enhancement. The ACF induced current would lead more vacancies in the treated sample, which promoted the diffusion in the substrate. The ACF should also intensify chemical reactions and diffusions in the boriding media with the energy from the ACF and the ACF's electro-magnetic stirring effect. More active boron-containing species formed and moved to the sample's surface to accelerate the formation of borides.