The phenomenon that the sugar-rich xylem sap ascending in the early spring is observed on some deciduous broad-leaved trees. We investigated the relationships between air temperature and sap exudation in Acer pictum Thumb. native to Chugoku Mountain. Exudated sap was collected and weighted at 1-2day intervals from February to April in 2016 and 2017. Also, snow condition, air temperature, sugar content and sugar composition of the sap were investigated. Sap exudation was observed on the day with daily maximum air temperature ranged 2.9-16.8°C and daily minimum air temperature ranged －10.4-－2.6°C. In both 2016 and 2017, substantial stem sap exudation occurred between early February and middle March. The sap sugar content and sucrose concentration were high in the early February and gradually decreased to the end of March in both year. Notably, high concentrations of glucose and fructose were found in late March. Differences in air temperature at which sap exudation was observed and sugar composition of sap exudate were not apparent between 2016 and 2017. It was suggested that the sap exudate had mutual relation to a temperature change.