Abstract: Dynamic mechanical properties of diacetate fiber with various moisture contents were investigated by DMA.Various relaxations of the fiber and their mechanisms were analyzed.The investigation showed that the glass-transition of diacetate fiber appeared at 184℃,and theβ*andγrelaxations were humidity-dependent.Theβ*relaxation is associated with the synergy movement between the hydroxyl groups and the water molecules binding with them,whereas it can be considered that the movement of water molecule binding loosely with non-esterified hydroxyl groups is related toγrelaxation.The broaderβrelaxation,which existed in DMA spectrum of cellulose,is tentatively assigned to local motions of the main chain(glucose unit),but the possibility of the synergy movement between lateral groups and main chain can not be excluded.