In hot-water molecular dynamics simulation at 370 K, four cellulose IIII crystal models, with different lattice planes and dimensions, exhibited partial crystalline transformations of (1 -1 0) chain sheets, in which hydroxymethyl groups were irreversibly rotated from gt into tg conformations, accompanied by hydrogen-bond exchange from the original O3-O6 to cellulose-I-like O2-O6 bonds. The final hydrogen-bond exchange ratio was about 95 % for some of the crystal models after 50 ns simulation. The corrugated (1 -1 0) chain sheet was converted to a cellulose-I-like flat chain sheet with a slightly right-handed twist. The 3D structures of the three types of isolated chain sheet models were optimized using density functional theory calculations to compare their stabilities without crystal packing forces. The cellulose Iβ (1 0 0) models were more stable than the cellulose IIII (1 -1 0) models. The optimized structure of cellulose IIII (1 0 0) models deviated largely from the initial sheet form. It was proposed to the crystalline transformation from cellulose IIII to Iβ that conversion of the chain sheet structure first take place, followed by sliding of the chain sheet along the fiber axis. © 2013 Springer Science+Business Media Dordrecht.