Abstract:The paper reports the changes in endogenous hormones in buds of on-year and off-year trees of longan (Dimocarprs longana Lour. cv. Fuyan)during differentiation period. It was shown that isopentenyl adenine (iPA)content in flower buds of on-year tree was noticeably higher than that in vegetative buds of off-year tree, while the contents of GA and ABA were to the contrary. It indicated that iPA was advantagous, GA and ABA were unadvantagous to flower bud differentiation. The treatment of PP333 promotedthe flower bud differentiation, shortened the length of inflorescence and increased the yield of fruit.