Abstract: Montmorillonite-modified carbon foams with a closed-pore structure were prepared by compressive molding of phenolic resin, phenolic hollow microspheres and montmorillonite, followed by thermosetting and carbonization at 800℃ under Ar flow. The effects of the montmorillonite content on the microstructure, compressive strength and thermal conductivity of the modified foams were investigated. Results show that the hollow microspheres, carbon matrix and montmorillonite combine more closely in the modified carbon foams than the unmodified one. Their compressive strength increases and the porosity decreases with increasing montmorillonite content from 0 to 7 wt.%. The highest compressive strength is 25.54MPa and the lowest thermal conductivity at 800℃ is 0.588W/(m·K) when the montmorillonite content is 7 wt.%.