The objective of this research was to enhance the dimensional stability of biocomposites containing agricultural waste using a heat-treatment method. For this aim, cotton stalk (CS) flour was treated at 150 or 180 degrees C for 30 or 60 min in atmospheric air. The ratio of softwood fiber to heat-treated (CS) flour in the biocomposites (medium-density fiberboards, MDF) with a density of 700 kg/m(3) was 75/25%. The MDF panels were made using standardized procedures that simulated industrial production at the laboratory. Heat treatment of the CS flour significantly enhanced the water resistance of the MDF panels such as thickness swelling and water absorption. An increase to 60 min of heat treatment at 150 or 180 degrees C resulted in a further reduction of the swelling properties compared to the standard treatment (30 min). However, the mechanical properties such as modulus of rupture, modulus of elasticity, and internal bond strength declined as the temperature and time increased. This study revealed that the dimensional stability of the MDF panels incorporated with heat-treated CS flour was better than that of the panels incorporated with untreated CS flour.