Abstract: The trial to investigate hormonal and sugar changes in tree peony buds associated with dormancy was conducted in the field at the Beijing Forestry University Experimental Site in China during autumn, winter and spring seasons (2009/2010 and 2010/2011), the periods of dormancy development and release. The experimental design was randomized complete block with three replications. The hormone and sugar levels were determined using the enzyme-linked immunosorbent assay (ELISA) technique and spectrophotometer, respectively. Winter temperature accumulated abscisic acid (ABA) and sugars in tree peony buds which most likely induced dormancy. Spring temperature, on the other hand, degraded ABA and sugars, and accumulated gibberellic acid (GA₃) that possibly released dormancy in tree peony buds indicating that environmental temperature was the key regulator of hormone and sugar levels that influenced bud dormancy and growth. The results suggest that accumulation of ABA, GA₃ and sugars in buds during dormancy or bud-break stage appears to be directly related to the degree of temperature experienced at that stage. While ABA and sugar accumulated with decreasing temperature, GA₃ accumulated with increasing temperature. It is likely that the reduction of ABA and sugars played an important role in bud dormancy release or alteration in bud growth of tree peonies. Seasonal patterns of sucrose and starch were almost the same in buds of the tested tree peony cultivars which contradicts previous studies suggesting converse relationship in terms of accumulation in winter. However, seasonal accumulation of endogenous compositions varies with cultivar. Among the investigated cultivars, ?Luoyang Hong? (LH) not only accumulated less ABA, GA₃ and sugars but also released bud dormancy earlier than the ?Zhao Fen? (ZF) and ?High Noon? (HN), suggesting that the level of these internal compositions in LH is less responsive to seasonal temperature change. The ability of buds to simultaneously accumulate ABA and sugar reserves while in dormant state may provide a significant adaptive advantage for peonies to survive the erratic climate, particularly in temperate regions, which could be one of the reasons for the geographically widespread of the genus Paeonia in the world.