A Ti-6Al-4V alloy was heat-treated to give two types of microstructures with different volume fraction of equiaxed alpha phase and lamellar (alpha + beta) microstructure. Disks were cut from the heat-treated rods and processed by quasi-constrained high-pressure torsion (HPT) at room temperature with an applied pressure of 6.0 GPa and torsional straining from 1/4 to 20 turns. The results show that there is a gradual evolution of homogeneity in microhardness and grain size with increasing numbers of revolutions in HPT such that the microhardness values attain a maximum constant value across the disk after processing by HPT for 10 turns and the measured equilibrium grain sizes after 20 turns are similar to 130 nm in Ti64-1 and similar to 70 in Ti64-2. The results show also that a larger fraction of lamellar (alpha + beta) in the microstructure of Ti-6Al-4V leads to a higher hardenability after processing by HPT.