Plasma copolymerization was carried out from the monomer mixtures of acrylic acid with hexamethylxdisilozane and hexametydisillazane, and the membranes composed of the Si-C and/or Si-O networks sustaining carboxylic acid group were fabricated. The carboxylic acid contents were dependent on the discharge power conditions as well as the monomer ratio, and carboxylic acid was introduced at the more density in the polymerization by plasmas under the moderate power conditions. The plasma polymer coatings were effective for the adsorption of lysozyme especially on the plasma copolymer films of acrylic acid. (C) 2003 Elsevier B.V. All rights reserved.