Ring-opening polymerizations of both 1,4-anhydro-3-O-benzyl-2-O-pivaloyl- (1) and 1,4-anhydro-3-O-benzyl-2-O-acetyl-alpha-D-xylopyranose (2) gave their respective (1-->5)-beta-D-xylofuranan derivatives. Subsequent removal of the protective groups gave stereoregular (1--5)-beta-D-xylofuranan for the first time. Polymerization of monomer 1 by PF5 gave 3-O-benzyl-2-O-pivaloyl-(1-->5)-beta-D-xylofuranan with [alpha](d)(25) -87.4 degrees and a number-average molecular weight of 16.9 x 10(3) (DPn = 55). Polymerization of monomer 2 by PF5 gave 3-O-benzyl-2-O-acetyl-(1-->5)-beta-D-xylofuranan with [alpha](D)(25) -121.1 degrees and a number-average molecular weight of 6.4 x 10(3) (DPn = 24). Removal of the acyl and benzyl groups gave nonnatural new stereoregular polysaccharide (1-->5)-beta-D-xylofuranan.