The formation mechanism of titanium boride functional nanoparticles by the radio frequency induction thermal plasma was investigated by experiment and numerical analysis. The mixed powders of titanium and boron were injected into the plasma and evaporated immediately, and then nanoparticles were produced through the quenching process. The nanoparticle products were characterized by phase composition and crystalline diameter. TiB2 was easily synthesized with a low powder feed rate in the boron-rich condition, because the molar ratio of evaporated and nucleated boron in plasma was enhanced. The prepared titanium boride nanoparticles had the average crystalline diameter ranging from 10 to 30 nm, and it was reduced with decreasing the powder feed rate and titanium content in the raw material due to abundant number of boron nuclei. This paper demonstrates the feasibility of the control of titanium boride nanoparticles' crystalline mean diameter and phase composition with different raw material condition in the RF induction thermal plasma synthesis. (C) 2011 Elsevier B.V. All rights reserved.