Abstract: In order to investigate the hot deformation behavior and microstructure evolution of Ti-5.5Al-3Nb-2Zr-1Mo titanium alloy during hot deformation, the hot compression tests were carried out under the deformation temperatures of 855-1015 ℃, strain rates of 0.001-10 s^-1 and deformation degree of 60% on a Gleeble-1500 thermo-mechanical simulator. The Arrhenius-type constitutive equation of the titanium alloy was constructed. The microstructure and grain boundary character after hot compression were analyzed. The results show that the titanium alloy shows obvious dynamic softening behavior during hot compression, and the peak stress increases with the decrease of the deformation temperature and the increase of the strain rate. The activation energy of hot deformation in the（α+β） two-phase region is calculated as 541 kJ/mol, and the activation energy of hot deformation in the β single-phase region is 243 kJ/mol. The microstructure evolution during hot deformation is sensitive to the deformation temperature and strain rate. During the deformation in the（α+β） phase region, incomplete dynamic recrystallization of the α phase occur, associated with the formation of a large number of high-angle grain boundaries.Meanwhile, the dynamic recovery of β-phase is the main softening mechanism for the alloy during the deformation in βsingle-phase region. An interlaced acicular α metallographic structure appears in the subsequent water quenching process.