The superplastic tensile deformation behavior and structural evolution of two kinds of α+β titanium alloys were investigated in this paper, one is a new high strength high toughness Ti alloy with damage tolerance called TC21, and the other is a new superplastic Ti alloy so called Ti-SP2500. The results indicated that TC21 alloy has good superplasticity at the temperature from 720 to 960 and with the strain rate of 5.510-5s-1∼1.110-2s-1. On the optimal superplastic condition, the maximum elongation is over 1300%. During the superplastic tensile deformation, the dynamic recrystallization occurs in deformation zone of the specimens and the superplasticity is improved. Ti-SP2500 alloy has good superplasticity at the temperature from 720°C to 800°C and with the strain rate of 6.67 10-4s-1∼1.1110-2s-1. The maximum elongation for Ti-SP2500 alloy will exceed 2200% at 780°C with the strain rate of 5.5610-3s-1. Its superplastic deformation mechanism is controlled by grain boundary sliding, and the grain deformation and dislocation creep has the coordinating action.