The knowledge of human bone viscoelasticity is an important issue for defining semirigid calcified tissues implants. A very sensitive technique was used to investigate bone viscoelasticity: the thermally stimulated creep method. A study of demineralized human bone was performed to determine the molecular origin of bone viscoelasticity. The thermally stimulated creep spectra of bone and demineralized bone, at the hydrated state, present a similar shape with one main retardation mode located at -133 and -120 degreesC, respectively. This mode is shifted toward higher temperatures after dehydration, revealing the existence of another mode at around - 155 degreesC. The analysis of elementary spectra of bone and demineralized bone has shown that retardation times follow an Arrhenius equation, and that two compensation phenomena are observed with comparable compensation parameters. The first compensation phenomenon, which corresponds to the main retardation mode, was attributed to motions of water molecules located inside the collagen triple helix. The second compensation phenomenon, which reveals the existence of another relaxation mode at higher temperatures, was assigned to movements of hydrophilic side chains bound to water molecules. As for the mode observed at around -155 degreesC, it was associated with motions of aliphatic side chains. Overall, bone viscoelasticity originates from the organic matrix.