Abstract: The poplar wood powder (PWP) was surface modified by 4,4'-methylenebis (phenyl isocyanate)/γ-aminopropyltriethoxysilane(MDI/KH550) in N,N-dimethylformamide (DMF). The effects of material ratio, reaction temperature, reaction time and dosage of catalyst on the reaction were investigated. The chemical structure and surface properties of modified poplar wood powder were characterized by contact angle measurement, elemental analysis, FT-IR, 13C CP-MAS NMR and SEM. The results showed that the weight percent gain (W) of MDI/KH550 modified PWP increased by 40-60% when MDI reacted with PWP in molar ratio of 2:1 at 120 ℃ for 2 h, and the catalyst had no appreciable effect on the modification reaction. The hydrophobicity of modified PWP was improved.