Wood’s chemical composition has a close relationship to its mechanical properties. Therefore, chemical analysis such as FTIR spectroscopy offers a reasonable non-destructive method to predict wood strength. Pine (Pinus densiflora) specimens were thermal-treated in different conditions (aerobic and anaerobic) and evaluated by 3-point bending test for modulus of rupture (MOR) and by FTIR spectroscopy for chemical composition. Density and moisture content changes were also assessed in this study. The result showed that both density and equilibrium moisture content at 20 ◦C with 65 % humidity change little at low treatment temperatures, but they decrease at high treatment temperatures and when treated in the presence of oxygen. The MOR was improved by the reactions that occurred, including cellulose crystallisation, lignin condensation and cross-linking, whereas it was decreased by degradation reactions. The MOR were well predicted by two FTIR peak at 1318 cm-1 (relating
to CH2 bond and condensation of G-ring of lignin), and at 1730 cm-1 pertaining to changes to carbonyl groups in hemicelluloses) and density. It was concluded that FTIR spectroscopy provides a suitable method for wood non-destructive mechanical testing.