This paper reports on the physical and mechanical properties and decay and termite resistance of fiberboard panels made from pine and beech treated with N'-N-(1, 8-Naphthalyl) hydroxylamine sodium salt (NHA-Na), borax, and boric acid at varying loadings. The panels were manufactured using 10 percent urea-formaldehyde resin and 1 percent NH4Cl. Mechanical and physical tests demonstrated no statistically significant reduction in modulus of rupture of specimens treated with borax + NHA-Na compared to untreated control specimens. Similar results were obtained for modulus of elasticity for all treatments at concentrations of 1 percent and lower. Internal bond values of treated specimens were somewhat reduced in comparison with values of control specimens, but higher than DIN EN 622-5 standards for medium density fiberboard. Treated specimens showed increased resistance against the decay fungi Fomitopsis palustris and Trametes versicolor and the Formosan subterranean termite Coptotermes formosanus Shiraki. For individual treatments, specimens treated with borax and boric acid showed lower weight loss compared to specimens treated with NHA-Na alone. The possible synergy of borax + NHA-Na resulted in low water absorption, high modulus of elasticity, and increased resistance to decay and termites.