Abstract: The expansive soil in Zigui County is another discovery in the Three Gorges Reservoir region after the discovery of expansive soil in Wushan County,Fengjie County and Xingshan County,which discloses the locality feature of the expansive soils.The expansive soil,the same as the others in the Three Gorges Reservoir region,develops in the special geo-environment and with the Diluvial-to-Pluvial genesis and relatively uniform structure.The expansive property is mainly determined by the montmorillonite in it,whose content is about 18.67% by test and exhibiting in the form of mixed-layer mineral illite/ montmorillonite(I/S) with middle mixed-layer ratio.The soil has high plastic limit,high liquid limit and low anti-shearing intensity,and reaches the national and international standards and limits on expansive soil.