In this article, the effects of bio-oil and epoxidized linseed oil (ELO) on water absorption, tangential swelling, decay and insect resistance, thermo-gravimetric analysis, and mechanical properties of treated wood samples were studied. The bio-oil used in this article was by-product of ThermoWood thermal modification process. Linseed oil and hydrogen peroxide were used to prepare ELO. The results indicated that the samples treated with bio-oil had lower water absorption than that of the control group. The second treatment with ELO significantly reduced further the water absorption. The decay resistance of treated wood samples with 20% of bio-oil against brown (Coniophora puteana) and white rot (Trametes versicolor) fungi was very high. According to the insect test results, increasing bio-oil concentration from 10% to 20% significantly decreased surviving rate of Hylotrupes bajulus. Thermo-gravimetric analysis showed that all treated samples had higher initial deterioration temperature than that of the control group. Regarding the wood strength, the impregnated bio-oil generally reduced the mechanical properties of wood except modulus of elasticity (MOE). (c) 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1562-1569, 2013