Mixtures of copper, titanium and boron powders were mechanically alloyed for various periods of the milling by using an attritor ball mill. Microstructural changes of mechanically alloyed powders through the processing were investigated. Structure consisting of extremely fine grain is formed in either case of the mixed powders by the processing for long milling time. The refinement of Cu-Ti powder is accelerated by additions of boron and TiB2 powders. Solubility of titanium in copper phase of powder is about 2mol% after the mechanical alloying for more than 72.0ks, regardless of content of titanium. Intermetallic compound TiB2 is formed in the Cu-Ti-B system by the solid state reaction of titanium and boron during the processing for long milling time.