Plasma copolymerized methylmethacrylate and tetramethyltin [PP(MMA–TMT)] was prepared using an inductively coupled gas flow‐type reactor. The atomic ratio of tin to carbon (Sn : C) in PP(MMA–TMT) was varied from 0 to 0.15 by changing the gas flow rate ratio of both TMT and MMA monomers. The characteristic of PP(MMA–TMT) as a resist was evaluated in dry lithography processes, in which the resist was exposed to radiation of CuKα(main wavelength: 1.54 Å) and x‐ray imaged pattern in the resist was developed by Ar–20% O2mixture gas plasma using a parallel plate electrode‐type reactor. The sensitivity of positive resist was defined by the minimum dose rate that the resist in the exposed part was etched off when the remaining thickness at the unexposed part became about 38% of the initial film thickness under the plasma development. PP(MMA–TMT) resist showed the highest sensitivity of 8 J/cm2at Sn : C of 0.046. The molecular structure of PP(MMA–TMT) film was investigated by electron spectroscopy for chemical analysis (ESCA) and infrared (IR) analysis and discussed in relation to its quality as a resist.