Noble metal borides RuB1.1, RuB2 and Ru2B3 have been synthesized by mechanical alloying and high pressure sintering methods using ruthenium (Ru) and boron (B) powders as raw materials. The crystal structures of borides were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results shown that only RuB1.1 with hexagonal crystal structure was synthesized during the ball milling process, the orthorhombic RuB2 was synthesized under high pressure (5 GPa) and high temperature (1000 degrees C) conditions, while the hexagonal Ru2B3 can be synthesized under 5 GPa and 1200 degrees C. The mechanism of synthesis for the ruthenium borides (RuBx) are discussed in details. (C) 2015 Elsevier Ltd. All rights reserved.