Abstract: In order to explore the improving effect of SiO₂ on the properties of fast-growing plantation poplar wood, two kinds of SiO₂/poplar wood composites were prepared by sol-gel and impregnating silicasol method, respectively. The performances of microscopic morphology, structure composition and thermal degradation about the composites were characterized and evaluated by SEM, XRD, FTIR and thermal analysis. The results show that SiO₂ has a wide distribution in the vessels, wood fibers and gaps between wood cells in the wood substrate, and its contact with wood cell walls in the composites fabricated by means of sol-gel is tighter which presents more effective filling and combination. The diffraction intensity and crystallinity in wood cellulose of SiO₂/poplar wood composites exhibit a decreasing trend resulting from the introduction of SiO₂, and the variation of (100) crystal surfaces in the composite fabricated by sol-gel is more obvious. The pyrolysis temperatures of SiO₂/poplar wood composites decrease from 420 ℃ to 380 ℃ with a narrowing of pyrolysis reaction, accelerating the occurs of wood carbonization to protect wood substrate from burnout adequately in some extent.