Abstract: To study the relationship between changes of endogenous hormones and sterility of Lagerstroemia indica, this paper measured the dynamic changes of 4 kinds of endogenous hormones (IAA, GA3, ZR and ABA) contents by the method of ELISA during the stage of floral organ differentiation and pollination of sterile L. indica Xiangyun and fertile L. indica. The results showed that there existed great differences on the changes of endogenous hormones between them. The sterile one had higher levels of contents of GA3, ABA and IAA than the fertile one at the beginning of the floral organ differentiation stage. With the further development of floral organ, the content of ZR in sterility was lower than that in the fertile one, while GA3 was higher. The contents of endogenous hormones changed in the whole pollination stage, and the content of GA3 in the sterility was lower. So the abnormal changes of endogenous hormones during the floral organ differentiation and pollination affected the development of floral organ and fruit of the sterile L. indica Xiangyun.