The microstructure evolution and mechanical properties of 51.1Zr-40.2Ti-4.5Al-4.2V alloy during tensile deformation at room temperature were studied. The results show that the phase transformation from β to α" phase were observed in the process of tensile deformation at room temperature, and the volume fraction of the α" phase decreases with the increase of the tensile rate. The existence of the α" phase has an obvious effect on the mechanical properties of the alloy. At the tensile rate of 0.3 mm/min, the trigger stress (TS), ultimate tensile strength (UTS), elongation (EL) and elastic modulus (EM) were 770.06 MPa, 1168.60 MPa, 14.96% and 64 GPa, respectively. TS and EM increased with the increase of tensile rate, while UTS and EL decreased. Three different stages were presented in the curve of work hardening rate. Especially, the second stage was obviously affected by the α" phase. At a given strain, the work hardening rate at the second stage is gradually decreased with increasing tensile rate. When the tensile rate was 0.3 mm/min, the fracture morphology of the alloy was composed of a large number of dimples and a small number of quasi-cleavage planes, which show a typical feature of plastic fracture. With the increase of the tensile rate, the fracture mode of the alloy changed from plastic fracture to brittle fracture. This is mainly due to that the volume fraction of the α" phase decreases with the increase of the tensile rate.