Abstract: Gas products and chemical vapor deposition kinetics of pyrocarbon (PyC) formed during pyrolysis of a propylene/argon mixture in the range 700-1 200 ℃ were analyzed by out-line gas chromatography coupled with mass spectrometry and by an insitu magnetic suspension balance, respectively. More than 30 components were identified. Benzene was the main product, substituting for naphthalene as the temperature increased. PyC was formed with an apparent activation energy of (137±25) kJ/mol, assumed to be controlled by the acetyleneforming reaction from 800 ℃ to 1 000 ℃. Whereas, above 1 000 ℃, the deposition behavior was representative of a combination between gas phase diffusion from the bulk flow to the solid surface and gas phase nucleation. Reaction models describing homogeneous gas phase PyC deposition reactions were derived. On the basis of these results, a reaction path scheme of PyC formation from propylene was proposed.