It was found that a β-fructofuranosidase produced by Microbacterium sp. H-1 has potent trans-β-fructofuranosylation activity from sucrose (donor). By means of this enzyme system, rebaudioside A (RA), the second major sweet steviol glycoside of the leaves of Stevia rebaudiana, was subjected to transfructosylation, affording a mono-β-fructofuranosylated product (RA-F) in a high yield. The structure of RA-F was elucidated as β-D-fructofuranosyl-(2→6)-β-D-glucopyranosyl ester of steviol-13-O-[β-D-glucopyranosyl-(1→2)]-[β-D-glucopyranosyl-(1→3)]-β-D-glucopyranoside. Some improvement in the quality of sweetness was observed for RA-F.