Changes in physical and chemical properties of oak sawdust were investigated by depth and time for 46 days duringthe fermentation process of 33 tons of the sawdust for oak mushroom cultivation. The degrees of change in the properties of thesawdust differed depending on the depth and fermentation period. Most of the physical-chemical properties except temperatureand pH gradually changed during the fermentation. The temperature change was highly sensitive to the environment at thesurface sawdust to 20 cm depth, while it gradually increased to the maximum 58.9oC at 40~100 cm depths in 12 days andslowly to the maximum at 150 cm depth in 24 days. The moisture content of the sawdust decreased gradually from 31% to26.5~28.0% in 24 days. Of the chemical properties during the fermentation, pH generally rose from 5.2 to 5.6, but it decreasedto 4.4~4.7 at 150 cm depth in 16 days. While the carbon content of the sawdust was 68~70% without significant change,nitrogen content increased from 0.22% to 0.25% and thus C/N ratio gradually lowered from 320 to 280. P content in thesawdust gradually increased from 0.005% to 0.022% for 46 days. Osmotic concentration of the hot water extract of the sawdustvaried 41.5~44.2 mmol/kg without significant change by the depth and time. The starch particles within initial ray parenchymacells of sawdust decreased and fungal hyphae formed on the surface of the sawdust granules and within xylem vessel cells in 35days. The effect of the sawdust fermentation on oak mushroom cultivation needs continued research.