In this work, we present and characterize a microwave plasma microtorch that can support the formation of diamond nanoparticles (DNPs) in the gas phase when using hydrogen-methane as a precursor gas. We first showed how the non-equilibrium character of the plasma obtained in this microtorch ensures enhanced H-atom, C 2 and CH 3 production at moderate gas temperatures levels that which provides thermal stability of DNPs. The material characeterization by TEM, Raman and EELS spectra confirm the presence of substantial amount of diamond phase in the carbon dust particles collected from the plasma phase. Investigation of the effects of injected MW power on the process characteristics showed a direct correlation between enhanced C 2 production and appearance of diamond phase, which points out to the critical role of C 2 as far as gas-phase nucleation of DNPs is concerned.