The chemical vapor deposition (CVD) of boron carbide was investigated on a tungsten substrate from a gas mixture of BCl3, H-2, and CH4 in a dual impinging-jet reactor that was connected to an FT-IR spectrometer for on-line analysis of the reactor effluent stream. During CVD of boron carbide, the formation of BHCl2 was experimentally verified, and beta -rhombohedral B4C was formed. Conversion to boron carbide was found to increase with an increase in the BCl3/CH4 ratio. However, conversion to dichloroborane decreased with an increase in the BCl3 concentration in the inlet gas stream. Kinetic data showed that the B4C formation reaction rate is proportional to the 1.85 power of the BCl3 concentration.