The objective of this study was to investigate the influence of acetylation on mechanical properties of the medium density fiberboard (MDF). Industrial fibers were acetylated in a reactor at 120°C, with acetic anhydride and without any catalyst to achieve weight gains 5, 9 and 16% (WPGs) and tested with FTIR spectroscopy. The test boards were made based on target density 0.7g/cm3, with 10 mm thickness under 30 bar pressure at the temperature of 180°C for 5 min press time. Internal bonding (IB) and module of rupture (MOR) and elasticity (MOE) of the boards were determined. The results showed that IB and MOR and MOR were reduced by acetylation.