Chondroitin sulfate (CS) is as ulfated polysaccharide that playsessential physiological roles.Here,wereport an enzyme-based method for the synthesis of al ibrary of 15 different CS oligosaccharides.This library covers 4-O-sulfated and 6-O-sulfated oligosaccharides ranging from trisaccharides to nonasaccharides.Wealso describe the synthesis of unnatural 6-O-sulfated CS pentasaccharides containing either a6 -Osulfo-2-azidogalactosamine or a6 -O-sulfogalactosamine residue.T he availability of structurally defined CS oligosaccharides offers an ovel approach to investigate the biological functions of CS.