AYRILMIS N, JARUSOMBUTI S, FUEANGVIVAT V & BAUCHONGKOL P. 2011. Effects of thermal treatment of rubberwood fibres on physical and mechanical properties of medium density fibreboard. This study evaluated effects of thermal treatment of rubberwood fibres at elevated temperatures on physical and mechanical properties of medium density fibreboard (MDF). MDF panels were manufactured from untreated rubberwood fibres and fibres treated at three different temperatures (120, 150 or 180 degrees C) for 15 or 30 min in a laboratory autoclave. The thickness swelling of the panels decreased with increasing treatment temperature and time while mechanical properties, flexural properties, internal bond strength and screw withdrawal resistance, decreased. Results of the internal bond strength showed that thermal treatment of rubberwood fibres increased the hydrophobicity of fibre surfaces, which reduced the adhesion and penetration of the urea-formaldehyde resin. In general, all panel types met the general purpose use requirements of EN standards. MDF panels made from thermally-treated rubberwood fibres at 180 degrees C for 30 min appeared to be a practical choice for applications requiring low thickness swelling.