The effect of calcium hexa boride (CaB6) on microstructure and mechanical properties of powder metallurgy CP-Ti and Ti-6Al-4 V was studied. CaB6 can scavenge the solid solution O during sintering, producing Ca-Ti-O and TiB second phases. These Ca-containing particles precipitate in the grain boundary to inhibit grain growth, resulting in the formation of equiaxed alpha grain in CP-Ti and a fine and homogeneous basket-weave structure in Ti-6Al-4 V. Compared to CP-Ti, the a phase of Ti-1CaB(6) reduces from 178 mu m to 36 mu m. With respect to Ti-6Al-4 V, the alpha + beta lamellae length reduces from 203 to 38 mu m. The sintered relative density is also improved with O scavenging. The relatively density increases to 99.3% in Ti-0.2CaB(6) and 98.8% in Ti-6Al-4 V-0.1CaB(6). The same reason may also account for the improved ductility. Overall, an addition of 0.2 wt% CaB6 in CP-Ti and 0.1 wt% CaB6 in Ti-6Al-4 V can obtain better comprehensive tensile properties (UTS = 665 MPa, YS = 604 MPa, EL. = 15% for Ti-0.2CaB(6); UTS = 944 MPa, YS = 903 MPa, EL. = 9% for Ti-6Al-4 V-0.1CaB(6)). (C) 2018 Elsevier B.V. All rights reserved.