A novel water-soluble dextran was synthesized from maltodextrin by cell-free extract of Gluconobacter oxydans DSM 2003. The dextran was purified by size exclusion chromatography, and the structure was determined by Fourier transform infrared spectroscopy, nuclear magnetic resonance, and gas chromatography-mass spectrometer. Based on the spectral data, we found that the dextran contained only d-glucose residues. The ratio of nonreducing end glucopyranosyl (Glcp) to 6-linked Glcp to 4,6-linked Glcp was estimated to be 8.62:78.79:12.59 by methylation analysis. This result indicated the existence of a small proportion of alpha(1,4) branches in alpha(1,6) glucosyl linear chains. Here, we reported the first time a novel dextran was synthesized by G. oxydans DSM 2003.