An experimental and computational study is conducted for the Si-based functional nanoparticle fabrication in an inductively coupled thermal plasma reactor. In the computational study, the improved multi-component co-condensation model with nodal discretization is proposed to clarify the nanoparticle growth mechanism in the consideration of coagulation and thermophoresis as well as simultaneous co-condensation. The nanoparticle growth by nucleation and co-condensation completes approximately in 12.6 ms for the Mo-Si system and in 5.0 ms for the Ti-Si system. Mo nanoparticles grow in advance, and then Si vapour condenses on the Mo nanoparticles in the Mo-Si system, while vapours of Si and Ti simultaneously co-condense following Si nucleation in the Ti-Si system. A smaller number of larger nanoparticles are created with an increase in the powder feed rate. When the silicon content in the feed powders is 66.7%, nanoparticles of MSi2 (M ≤ Mo, Ti) are fabricated as the main product. Nanoparticles of Ti5Si3 are mainly synthesized in the case of the silicon content 33.0%. In the experiment, the nanoparticles are successfully fabricated and examined by x-ray diffractometry and transmission electron microscopy. The experimental and computational results show good agreement in the size distribution and the composition.