Plasam polymerization of hydrocarbon/sulfure dioxide mixtures, C2H/SO2, C2H4/SO2, and CH4/SO2 mixtures, was investigated to obtain thin films containing sulfonic acid groups. Plasma polymerization of C2H2/SO2 and C2H2/SO2 mixtures gave filmlike products but that of the CH4/SO2 mixtures did not. The plasma polymers possessed much amount of sulfur and oxygen moieties with hydrocarbon chains. The sulfur moieties involved thio, sulfite, and sulfonic acid groups. This groups was a main product and reached 70–80 mol % of the total sulfur moieties. The remains (20–30 mol %) were sulfonic acid and sulfite groups. The oxygen moieties were hydroxyl and carbonyl groups with small amount of carbonxyl groups. The plasma polymers showed and hydrophilicity (the surface energy was 54–56mN/m) and good antithrombogenity.