Mechanical alloying teratment of mixtures of elemental copper, titanium and boron powders containing various amounts of boron was carried out by using high energy ball mill. For comparisons, the treatment of mixture of alloy powder prepared from Cu-8mass%Ti cast and the boron powder was also carried out. Influence of boron content on the formation of boride titanium during the mechanical alloying and subsequent heat treatment was examined. In the powder prepared from the mixture of elemental powders, a-solid solution and nonequilibrium Cu-Ti phase are formed during the mechanical alloying. When the powder was heat-treated at 1173K, the noncruilibrium phase disappears, and equilibrium Cu3Ti phase and ultrafine spherical boride titanium particles are formed. Ti3B4 and TiB2 particles are formed in the case of mixture with low contents of boron, but only TiB2 is formed from the mixture with high boron contents. The nonequilibrium Cu-Ti phase is also formed by the mechanical alloying in the powder prepared from the Cu-Ti cast, but the quantity of that phase is less than that of the powder prepared from the mixture of elemental powders.