We have investigated the properties of gold metal/polymer composite thin films. These composite films are prepared by DC plasma sputter deposition using an argon and methane gas mixture. A high-purity gold metal was used as a sputtering target. Sputtered gold atoms do not make compounds with hydrocarbon in plasma, because gold is a non-reactive metal. Additionally, both plasma polymerization of the methane and deposition of the sputtered gold atoms appear on the substrate. Consequently, composite films are formed. Composite films can be changed from metallic to dielectric according to the preparation conditions. There are main 2 parameters, i.e., the sputtering voltage and the partial pressure of the methane. It is necessary that the sputtering voltage is low, under 300 V in this work, because bombardment of the high-energy particles occurs to suppress the polymer growth on the substrate. It is found that the desired structure and properties of the composite thin films can be obtained, by suitable adjustments of the partial pressure of the methane, at a sputtering voltage of 300 V.