The double treatment of tetraphenylborate sodium salt [(C6H5)4BNa] with potassium chloride was investigated by impregnating them into sapwood specimens of Cryptomeria japonica to form the insoluble salts of tetraphenylborate potassium (Lin et al., 2001). The reduction of boron retention in wood specimens after the leaching test indicated good fixation of the boron compounds. The double treatment also showed an excellent efficacy effect against both C. versicolor and T. palustris (Lin et al., 2001).