Collagen is the major component of most connective tissues in animals. The structure of the helix and axial molecular packing within fibrils is well documented. Less is known about the structural alterations that occur on drying and the compounded changes that occur on dehydrothermal treatment. The structural properties of collagen and its supramolecular architecture are of importance in these states, since many of the industrial applications of collagen-based materials involve dried collagen or dehydrothermally treated collagen. The effects of drying and thermal treatment of collagen can be observed by X-ray diffraction, the changes in the diffraction pattern relate to changes in the axial packing of collagen molecules as dehydration occurs. The meridional diffraction series becomes truncated indicating induced structural disorder, the spreading of diffraction features indicate that the molecular orientation is altered for some of the collagen chains or portions of collagen chains within a fibril. Dehydrothermal treatment of parchment collagen for up to 24 h reduces the axial periodicity of the collagen fibril from 64.5 to 60.0 nm. Analysis of the X-ray diffraction data shows the possible alterations in molecular packing that may explain the structural changes.