AbstractBy means of x‐ray fiber diffraction, it has been found that xylan diacetate crystallizes with two chains or four residues in a monoclinic cell (space groupP21):a= 7.64,b= 12.44,c(fiber axis) = 10.31 Å, and γ = 85°. Pairs of residues are related by a twofold screw axis in thecdirection. Based on the observed fiber repeat and chain symmetry, the probable conformation of a pair of xylose diacetate residues joined via a β‐1,4′ linkage has been obtained by energy minimization methods. The conformations corresponding to a threefold screw axis and a twofold screw axis along the chain have been compared and the reason why xylan diacetate assumes a twofold screw axis seems to be due to intermolecular packing effects rather than intramolecular non‐bonded i