The Ti6Al4V-xB(wt.%,x=0,0.05,0.1,0.15)alloys were prepared at 900 ℃ for 2h by non-consumable melting and suction casting. In this study, the effect of Ti6Al4V-xB alloys with doping different B proportion on as-cast microstructures and mechanical properties is analyzed. The results show that the addition of boron impacts the solidification process of titanium alloy. The enriched B in solid-liquid frontier retarded the growth of initial β-Ti and was effective to promote grain refining. When the boron proportion was more than 0.1%, TiB phases precipitated from liquid. The ultimate strength of Ti6Al4V-xB alloys increased with the proportion of B (893 Mpa to 966 Mpa), which are attributed to grain-refinement and precipitation strengthening. The change of alloy plasticity is first increases and then decreases, about increasing 15% of Ti6Al4V-0.05B alloy and about decreasing 50% of Ti6Al4V-0.1B and Ti6Al4V-0.5B. This is because the fragile precipitated-phase of TiB is formed , which can cause the crack-sensitive zone.