The surface of the poly(monochloro-para-xylylene) (parylene-C) films after O2 plasma and successive Ar and NH3 plasma treatment was investigated using a contact angle and an X-ray photoelectron spectroscopy (XPS) measurement. In this work, it was confirmed that the polymer hydrophilicity after the O2 plasma treatment was sharply increased due to the formation of the highly oxidized surface layer. It was shown that exposure in an ammonia plasma led to the formation of nitrogen-containing groups on the polymer surface. It was found that both Ar and NH3 plasma treatment of the preliminary oxidized polymer led to the moderate extension of the water contact angle due to the decrease of the oxygen-containing polar groups' concentrations on the parylene surface.