Abstract: In order to know completely the microstructure of wood-silicon dioxide composite,the authors analyzed the relationship between cell wall expansion percentage and weight gain percentage(WGP),and the dimensional changes during moisture absorption treatment.We used the following techniques or instruments in our analyses: Xray diffraction(XRD),scanning electron microscopy(SEM) and energy dispersive X-ray analyzer(EDAX).Resultsincluded: 1) WGP was proportional to the moisture content of pretreated wood.Cell wall expansion percentage increased with the increase of WGP and tangential cell wall expansion percentage was higher than radial expansion.There was a slightly negative correlation between the percentage of dimensional change and WGP during the moisture absorption treatment.2) SEM analysis showed that silicon dioxide occupied free space of wood.EDAX analysis showed that silicon dioxide was found in cell wall of wood for the air-dried and moistening pretreatment of wood,and in both cell wall and cell cavity for the water saturated wood.The percentages of quality silicon in wood-silicon dioxide composite prepared from air-dried,moistening and water saturated wood were 4.11%,9.22% and 17.07%.3) XRD analysis showed that silicon dioxide was also found in cell wall of wood.Its crystallinity decreased with an increase of silicon dioxide content in wood-silicon dioxide composite.