The objective of this study is to reveal the sintering mechanism of mixed Ti-6Al-4V powders considering the densification and the homogenization between Ti and Al/V particles. It is found that the addition of master alloy particles into Ti enhances densification by the migration of Al into the Ti matrix prior to the self-diffusion of Ti. However, as Ti particles become coarser, sintering of the powders appears to be retarded due to slower inter-diffusion of the particles due to the reduced surface energies of Ti. Such phenomena are confirmed by a series of dilatometry tests and microstructural analyses in respect to the sintering temperature. Furthermore, the results are also consistent with the predicted activation energies for sintering. The energies are found to have decreased from 299.35 to 135.48 kJ·mol^-1 by adding the Al/V particles because the activation energy for the diffusion of Al in α-Ti (77 kJ·mol^-1) is much lower than that of the self-diffusion of α-Ti. The coarser Ti powders increase the energies from 135.48 to 181.16 kJ·mol^-1 because the specific surface areas of Ti decrease.