Two-dimensional numerical analysis is conducted to investigate the spatially complicated formation of nanoparticles in an induction thermal plasma (ITP) with counterflow cooling. The effects of convection, diffusion, and thermophoresis as well as nucleation, condensation, and coagulation are taken into account. It is clarified that counterflow cooling leads to effective conversion of vapor into nanoparticles. Furthermore, the growth mechanisms of the nanoparticle formation for six kinds of materials (B, Cr, Fe, Mo, Pt, and Si) are also studied. As the result, their dominant processes are revealed. (c) 2007 Elsevier B.V All rights reserved.