Abstract In this study, we prepared plasma polymerized styrene films, using the Ar and CH 4 mixture gas to investigate the potential effects of CH 4-containing reactive carrier gas on the plasma polymerized films. We investigated the variation of properties in the plasma polymerized styrene films prepared while changing the mixture ratio of CH 4 and Ar. From the results of Fourier Transform Infrared (FT-IR) which was performed to measure surface at the condition of changing the mixture ratio of Ar and CH 4, it was confirmed that the peak strength of products prepared under CH 4 containing carrier gas increased 1.5–2 times than that of products only under Ar gas and the deposition rates were linearly proportional to CH 4 mixture ratio. Molecular weight distribution was studied by Pyrolysis Gas Chromatography (PyGC). In this analysis, we found out that CH 4 carrier gas resulted in the increase of deposition rates and the drop of cross-linking degrees. And these effects are considered to have resulted from the influence of CH 4 reactive gas inflow in films. According to these results, in the case of plasma polymerization with reactive gas, it is possible to make the functional thin films which have properties of initial monomers and these films are suitable for sensors, opto-electric devices, and resist for lithography.