Abstract: Poor, delayed and ununiform bud break is a major problem for peaches in greenhouse. To clarify the mechanism of breaking bud dormancy in nectarine, the effect of three dormancy_breaking agents, which were applied to the surface of dormant buds in two_year old ‘NJ72’ nectarine (Prunus persica L. Batsch), was investigated. Treatment of intact nectarine plant with 2% thiourea(w/v) in November advanced flower bud break in the following spring by 20 days, while potassium nitrate was of no effect. But thiourea had a phytotoxic effect. The effect of ammonium nitrate was very similar to that of potassium nitrate, and flowering with the 2 nitrates was ununiform. In flower buds those were treated with dormancy_breaking agents, catalase activity was inhibited soon after treatment, whereas peroxidase activity increased, and changes of superoxide dismutase remained little. The rate of respiration in flower buds increased by chemicals during dormancy, among of which, the rate of the pentose phosphate pathway was also increased, while the rate of the Embden_Me yerh pathway decreased and the rate of tricarboxlic acid cycle changed little. The activity of glucose 6_phosphate dehydrogenase, the key enzyme in the pentose phosphate pathway(PPP), increased by dormancy_breaking agents, concomitantly with the activation of the pentose phosphate pathway.