Abstract: The temperature effect of soil is a hot issue in geotechnical engineering. However, the researches on the physical properties of soil in high-temperature environment over 100˚C are still insufficient. A kind of self-developed high-temperature heating apparatus is introduced, by which the variations of mass, moisture content, diameter and height of different soft clay samples from Shanghai are measured in the high-temperature environment of 105˚C, 120˚C, 150˚C and 200˚C for 2.5 hours or 4.0 hours. The variations of soil conductivity under 105˚C, 150˚C and 200˚C for 4.0 hours are also examined. The experimental results indicate that the volume and saturation of Shanghai soft clay decrease with the increasing temperature while the dry density of soil samples increases, and the trends of variations turn slow. The longer the heating time is, the greater the variation values of volume, saturation and dry density. The high temperature causes the increase of thermal conductivity for wet soil and dry soil and the thermal conductivity of dry soil is less than that of wet soil. Plastic deformation and heat hardening can be found for the soft clay in high-temperature environment, and the high temperature significantly affects the thermal conductivity of soft clay above 100˚C.