Multicomponent powders based on the B±C±N±Si system are of great interest as starting materials for sintering advanced ceramics and composites with improved properties. The square-wave modulation of the electrical power supplied to low pressure (<100 Pa) radio frequency (rf) plasmas has been shown as a suitable method to produce high purity silicon and binary powders, such as SiC, SiN and BN. The present study investigates the synthesis of silicon carbonitride (SiCN) nanometric powder in a plasma-enhanced chemical vapour deposition reactor, by rf glow discharge decomposition of CH 4 , SiH 4 and NH 3 gases at room temperature. The output of the rf source (13.56 MHz) was square-wave modulated at a period of 20 s with plasma-on times between 0.05 and 5 s. Transmission electron microscopy showed that the SiCN nanopowder was amorphous and that the average particle size increased from 9 to 100 nm as the plasma-on period increased. The chemical composition of the powder was analyzed by X-ray photoelectron spectroscopy and elemental analysis. Infrared spectroscopy revealed the presence of Si±C, Si±N, C±N and hydrogenated bonds. The infrared absorptions of hydrogenated bonds decreased as the plasma-on time increased, volume ratio with the increase in particle size.