Reaction behaviors of carbon disulfide and carbon dioxide in plasma were investigated and compared. It was found that carbon disulfide is very reactive in plasma to produce dark brown filmy polymers, but carbon dioxide does not give polymeric products at all. The difference in plasma behaviors of the two monomers can be attributed to the roles of sulfur and oxygen in the monomers. There is also some discussion on the spectro-scopic data of carbon disulfide polymers.