For all cellulose-like oligo- and polyglucans, beginning with the dimer cellobiose, a broad relaxation process at low temperatures is observed using the dielectric relaxation spectroscopy method. This relaxation has its molecular origin in orientational motions of the sugar rings via the glucosidic linkages. We investigated the dynamics of this main chain motion for beta (1-4) oligoglucans with 2, 3, 4, or 5 anhydro-glucose units (AGUs), as well as for beta (1-4) polyglucans having a degree of polymerization molecular weight averages (DPW) of 23, 37, 50, and 140 up to 3000. As a result we found that the activation energy (E-a) of the segmental chain motion has the lowest value (32 +/- 1 kJ/mol) for cellobiose, followed by passing through a maximum for a DP between 7 and 15 with E-a = 51 +/- 1 kJ/mol. Subsequently, the activation energy is decreased at a value around 44.8 +/- 1.2 kJ/mol for chains containing more than 100 AGUs. Obviously, from a distinctly molecular dimension (DPW similar to 100) the mean number of AGUs that take part in the local chain motions and cross-correlation between the motions of neighboring AGUs are nearly the same and the chain length has no influence on the segmental motion.