Many organisms attached on suspended oyster culture rafts, particularly filter-feeding animals can prevent growth of culturing oyster, because they are competing feeds with oyster in the same niche. In the present study, effects of steel wires coated with various materials on growth of the ubiquitous attached diatom Nitzschia sp. were experimentally examined to develop a better steel wire in terms of less attached organisms. The wire used were a normal zinc-galvanized steel wire, a polyethylene (ionomer resin)-coated steel wire, and magnesium oxide (HUS®)-added (3% and 5%) polyethylene coated steel wires. Following results were obtained, (1) all wires coated with different materials except the ionomer resin itself (as coating material) suppressed the growth of Nitzschia sp., and (2) 5% HUS®-added polyethylene-coated steel wire suppressed the growth of Nitzschia sp. greater than 3% added one did.