Abstract: Changes on the hormones in the leaves of Phyllagathis fordii during its flower bud differentiation stage weremonitored. Contents of 4 endogenous hormones, i.e., IAA, GA₃, ZR and ABA, were determined by using HPLC. The results showed that, at the completion of flower bud differentiation, the contents of GA₃ and ZR peaked, while IAA reached its lowest level in the leaves. In the mid of the differentiation stage, ABA maximized while GA₃ and ZR were low. The changes on these endogenous hormones highly significantly related to the flower bud differentiation. It was found that high level of ABA/IAA, ZR/IAA, and ZR/GA₃ratios in the leaves benefited the differentiation, whereas, high ABA/GA₃favored the induction of theflower buds.