Change in the deep supercooling (DSC) ability of xylem tissues of beech (Fagus crenata L.) twigs was detected by a differential thermal analysis (DTA). DSC abilities of xylem tissue shown as peaks of low temperature exotherms in DTA were about -30℃ in summer and -40℃ in winter. DSC ability of beech twigs in winter was lowered to about -30℃ by heat treatment at 60℃ for 10 min but was not lowered by heat treatment at 50℃ for 10 min. In order to find protein factors related to DSC ability, changes in the protein composition of xylem tissues caused by seasonal cold acclimation and heat treatments were analyzed by two-dimensional gel electrophoresis. About 350 protein spots were detected in the crude soluble fraction of xylem tissues in winter. Seventy-five protein spots were induced during seasonal cold acclimation. Fifty-six of the cold acclimation-induced proteins remained after heat treatment of xylem tissues at 50℃ for 10 min, and 12 of the 56 proteins were decreased by heat treatment of xylem tissues at 60℃ for 10 min.