Samples from alder (Alnus glutinosa L.) Gaertn. subsp. barbata (C.A. Mey) Yalt.) and southern pine (Pinus sylvestris L.) wood were impregnated with boric acid, borax and their mixed solutions according to ASTM D 1413-88 in order to determine their combustion properties. In this study, the fire resistance properties of wood treated with boron compounds were investigated. In addition, the models for each wood species and fire retardant solution were also determined. The results demonstrated that the lowest mass losses for both alder and southern pine specimens treated with a mixture of 5% boric acid and borax aqueous solutions were found to be 68.72% and 72.37%, respectively. It was found that 5% of borax was the most effective treatment in terms of lengthening the time of glowing. (C) 2007 Elsevier Ltd. All rights reserved.