In this paper we empirically examine the determinants on utilization of the Korea–ASEAN Free Trade Agreement (KAFTA) by employing a database provided by the Korea Customs and Trade Development Institute. We find that, although three effects, namely preferential margin (margin effect), rules of origin restrictiveness (ROO effect), and average export volume (scale effect), contribute to determining the utilization of the FTA, the scale effect has the greatest impact. Our results suggest that, since firms with relatively small volumes of trade are usually small and medium-size enterprises (SMEs), policy assistance for reducing administrative costs should be geared toward SMEs. Our results further indicate that policymakers should also try to negotiate more extensive tariff reductions on products not only where MFN rates are high but also where shipments are large.