This study aimed to examine that effects of year-round warmer condition to the growth and phenology of three-year-old Fagus crenata seedlings. This study was investigated under several controlled temperature conditions of outdoor temperatures altered by -1.0°C, ±0.0°C, +1.0°C, +2.0°C, +3.0°C. As a result, the terminal leaf buds elongation were almost the same under each warmer condition. But, the terminal leaf buds under warmer conditions required more cumulative temperature on growth. Photosynthetic rate had decreased under each warmer condition since June, 2002. Shedding leaves started under each warmer condition were almost the same, but, some shedding leaves under warmer condition were late on progress. And some seedlings under each warmer condition passed the winter without shedding leaves. Year-round warmer condition furthered to increase the percentages of the secondary flush. Some proleptic shoots under warmer condition were longer than Lammas shoots. There seemed that the growth and phenology of Fagus crenata seedlings were affected to year-round warmer condition.