Lightweight embankment tecchnology is increasingly being accepted for use in construction projects to solve soft ground problems. The most important advantages offered by this technology are reduced foundation soil improvement costs and reduced construction time due to the reduced loading on the ground. Previous work has shown the maximum temperature inside field test bodies ranged from 80～100℃, and the unconfined compressive strength of core samples of foamed mixture lightweight soils did not reach the design strength. At this time, we have focused on the effects of temperature increase of fill induced by cement hydration on the unconfined compressive strength of foamed mixture lightweight soils at a construction site. This paper describes the influences of high temperature curing on unconfined compressive strenghth and structure of foamed mixture lightweight soil at constant volume. We found that unconfined compressive strength decreases significantly from 20 to 90℃. The unconfined compressive strength cured for 28 days at high curing temperature (80 to 90℃) is about 50～60％ that of specimens cured at 20℃. The influences of high temperature curing on the structure of foamed mixture lightweight soil at constant volume are also investlgated.