Swelling behaviors of cellulose I-alpha and IIII crystals have been studied using molecular dynamics simulations of the solvated finite-crystal models. The typical crystal models consisted of 48 x 10-mer chains. For the cellulose I-alpha crystal, models consisting of different numbers of chains and chain lengths were also studied. The structural features of the swollen crystal models, including the cellulose I-beta crystal model reported previously, were compared. A distinct right-handed twist was observed for models of the native cellulose crystals (cellulose I-alpha and I-beta), with a greater amount of twisting observed for the I-alpha crystal model. Although the amount of twist decreased with increasing dimensions of the cellulose I-alpha crystal model, the relative changes in twist angle suggest that considerable twist would arise in a crystal model of the actual dimensions. In contrast to the swelling behavior of crystal models of the native cellulose, the cellulose IIII crystal model exhibited local, gradual disordering at the corner of the reducing end. Comparison of the lattice energies indicated that the cellulose chains of the I-beta crystal were packed in the most stable fashion, whereas those of the I-alpha and IIII crystals were in a metastable state, which is consistent with the crystallization behaviors observed. Upon heating of the native cellulose crystal models, the chain sheets of the I-alpha model showed a continuous increase in twist angle, suggesting weaker intersheet interactions in this model. The swollen crystal models of cellulose I-alpha and IIII reproduce well the representative structural features observed in the corresponding crystal structures. The crystal model twist thus characterizes the swelling behavior of the native cellulose crystal models, which seems to be related to the insolubility of the crystals.