Severe freezing events could be one of the crucial causes preventing the advance of alpine timberline. However,studies on the characteristics of freezing events across altitudes and vegetation types at high elevations are scarce. Based on the measurements of air and soil temperature for forests and shrubs across an Abies georgei var. Smithii timberline ecotone along a north-facing slope in the Sergyemla Mountains,southeast Tibet,we analyzed altitudinal variations of freezing events for different vegetation types during growing season based on two different definitions- canopy temperature and soil temperature. Results are as follows: 1) compared with canopy temperature of the growing season,soil temperature lagged behind nearly one month,and the length of growing season based on canopy temperature was significantly longer than that calculated by soil temperature for subalpine and timberline forests. 2) Although the growing season length varied between different definitions,there were more freezing events in Rhododendron shrubs in the growing season than in the subalpine and timberline forests,and the frequency for the former was 1 to 3 times more than the latter. Besides,the intensity was stronger and the duration was longer in Rhododendron shrubs than in the subalpine and /or timberline forests. Our results indicated that there were more growing-season freezing events in Rhododendron shrubs at high elevations,with their frequency,intensity,and duration all tending to strengthen with rising altitudes. This might result in the difficulty of seedling establishment above the timberline.