Mechanical alloying is the most perspective method for preparation of nanosized mechanocomposites in non-mixed liquid and solid metals. It is known that plastic metals get fragile in the presence of the liquid metal phase, and this phase spreads over the surface of solid metal due to good wettability. Temperature of milling bodies can rise by several hundred degrees in the high-energy planetary ball mill. Low melting metals, such as gallium, indium, tin, and bismuth can melt on the surface of the balls. So, a pair composed of liquid and solid metal can form in an activator. In such cases, it can be assumed that mechanical activation of metal systems with positive mixing enthalpies, can allow forming a morphologically metastable structure with unusually high concentration of inter-phase boundaries due to easy-melting component spreading along the boundaries of particles formed by comminution of the solid component. Nanosized mechanocomposites were prepared for Cu-Bi and Fe-Bi systems. The content of Bi in these systems must be lower than 3 at. (10 wt.)%. The obtained mechanocomposites represent nanosized particles of copper (or iron) coated with a layer of bismuth in 2-3 atoms. Mechanical activation of the formed composites leads to the formation of supersaturated solid solutions. (C) 2004 Kluwer Academic Publishers.