In the present study, synthesis and characterization of Ti6Al4V/Ti-B nanocomposite by mechanical alloying were investigated. For this purpose, the nanostructured Ti6Al4V matrix was obtained from elemental powders. The nanocomposite was then prepared by mechanical alloying of the Ti-Al-V-B powder mixture. Phase transformations, structural changes, morphological evaluations and hardness measurements of the samples were studied by means of x-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM) and microhardness measurements. Heat treatment of the powder product was performed for 5 hr at 1100?C in order to study thermal behavior. Bulk nanostructured Ti6Al4V alloy and Ti6Al4V/20wt%TiB nanocomposite samples were produced through cold pressing and sintering at 1100?C for 2 and 4 hr respectively. Wear tests were performed on bulk samples at ambient temperature with wearing velocity of 0.03 m/s under the applied load of 80 N. In the absence of B, the nanostructured Ti6Al4V alloy was formed by gradual diffusion mechanism of Al and V atoms in Ti lattice to form Ti(Al, V) solid solution after 10 hr milling. Prolongation of milling process up to 20 h leads to stabilization of ? phase in the ? matrix. A nanostructured Ti6Al4V alloy (2vol.% ? + 98 vol.% ?) with grain size of about 20 nm and hardness of about 600 Hv is obtained after 20 hr milling, meanwhile the hardness of the commercial plate of Ti6Al4V alloy was about 450 Hv. Hardness of the heat treated powder increased to about 950 Hv equal to that of heat treated Ti6Al4V alloy plate in the same condition. On the contrary, hardness of the pure Ti ball milled for 20 hr with grain size of about 30 nm was about 500 Hv and increase to about 600 Hv after heat treatment. Differences in thermal stabilities of the nanostructured Ti6Al4V alloy and pure nanostructured Ti could be assigned to the favorable effects of alloying elements on hardness. The Ti6Al4V-20wt% TiB2 nanocomposite was in situ synthesized after 40 hr milling followed by 1 hr heat treatment of Ti-Al-V-B powder mixture at 1100?C. Albeit, 40 hr milling was previously observed to be enough for the formation of TiB2 reinforcement from Ti-1.67at%B powder mixture by gradual diffiusion mechanism. Based on TEM observations of the nanocomposite powder, the grain size of the matrix and reinforcements were about 15 nm and 20 nm respectively, close to what was calculated by Williamson-hall formula. In search of thermal behavior of the powder product, heat treatment was done at 1100?C for 5 hr. Hardness increased from about 900 Hv to about 1830 Hv. As predicted, all TiB2 diffraction peaks had been replaced by TiB diffraction peaks due to the insufficient thermal stabilities of TiB2 in Ti matrix. Hardness of the bulk samples were about 830 Hv and 1030 Hv for Ti6Al4V alloy and nanocomposite, respectively. Relative density of the bulk nanostructured alloy and nanocomposite was 99.7 and 111% respectively. The bulk nanocomposite and the commercial alloy were the least and the most abrasive respectively. Wear behavior of the bulk nanostructured alloy was inferior to that of nanocomposite due to the absence of TiB reinforcements. Keywords Ti6Al4V alloy, wear, heat treatment, solid solution, formation mechanism, nanostructure