Abstract: The nano-SiO₂/cellulose composites were successfully synthesized by a sol-gel method using tetraethylorthosilicate (TEOS) as the silica precursor and cellulose in heterogeneous ethanol solution. The morphology，structure and thermal stability of the composite materials were characterized by TEM，FTIR and TGA. The influence of SiO₂ content on the mechanical properties of composites was discussed. The effect of basic catalyst ammonia on the content of silica in cellulose was studied.The results indicate that the elastic modulus of the composites increases with the increasing of SiO₂ mass fraction until 3.1% and then decreases，and the same is true of tensile strength when SiO₂ mass fraction is 10.6%. SiO₂ is incorporated into cellulose most effectively when the dosage of ammonia is 3.70×10^-4 mol/L.The hydrophobicity，thermal stability and mechanical properties of nano-SiO₂/cellulose composites in the heterogeneous system are also higher than those of the cellulosic materials.