Boron treatment was combined with vinyl polymerization to improve leaching resistance of boron from wood, as well as dimensional stability, biological and fire resistance of wood. Boric acid (BA) was impregnated into wood specimens [sapwood of Cryptomeria japonica D. Don, 20 (T) x 20 (R) x 10 (L)mm] as 1% aqueous solution prior to vinyl monomer treatment. Styrene (ST), methylmetacrylate (MMA) and their mixtures (50:50, v/v) were impregnated in the presence of a catalyzer and a crosslinker. Polymerization was conducted by heat radiation method at 90 degrees C for 4 h. Treated specimens were then subjected to decay and termite tests, as well as oxygen index (O.I.) determination. Anti-swelling efficiency (ASE;) and water absorption levels (WA) were also measured by standardized methods.