A new wood preservative system,in which soy protein was introduced to chelate copper cations,has been investigated.Experimental results indicated that soy protein HM90 greatly improved leaching resistance of copper cations fixed in ponderosa pine sapwood.By adding 8 and 16 kg/m3 of soy protein HM90 in ammoniacal copper sulfate solution,the retention of treated wood after leaching was 70% of initial retention on average.Because of the chelation of soy protein,the retention of copper protein after leaching was increased by 40% on average compared with that without protein.Moreover,lower concentration of copper sulfate was preferred for fixation of copper protein.However,in comparison with copper sulfate,there seemed no significant improvement for copper protein in ponderosa pine blocks on decay resistance to brownrot fungus Postia placenta. The threshold retention of unleached blocks treated with copper protein was as the same as the treated only with copper sulfate.Further investigations and improvement were suggested.