Disclosed herein are antisense DNA of a sweetpotato expansin (IbExpansin) cDNA, a plant transformation vector carrying the same, and a method for increasing storage root production using the same. The transgenic sweetpotatoes prepared using the antisense DNA of IbExpansin cDNA have storage root production increased by up to one and half times. Thus, the gene is useful in the generation of highly productive transgenic storage roots for the increase of bioethanol production.