Abstract: Microstructure at the different zones of linear friction welded TC11 and TC17 dissimillar titanium alloy joint were investigated to understand the mechanism of microstructural formation in the joints.The results showed that four different structures existed in linear friction welded joint, i.e.thermomechanically affected zone(TMAZ) in the region close to TC11 parent material, TMAZ the region close to TC17 parent material, weld zone in the region close to TC11 TMAZ, and weld zone in the region close to TC17 TMAZ.Although no dynamic recrystallization was observed in the TMAZ, the phase transformation would occur concurrently with material deformation during welding.In contrast, dynamic recrystallization occurred in the weld.Common prior-beta grains were formed at the original rubbing interface after welding.Under the conditions of 3 mm amplitude of oscillation, 40 Hz frequency of oscillation, 66.7 MPa friction pressure and absence of forge force, prior-beta grain size and alpha plate width increased with friction time increasing.