Abstract: The dynamic changes of plant hormone (IAA) were monitored by using ELISA technology during the formation of graft union. The changes of IAA in the compatible graft are comparable to the incompatible graft at the early stages of development of graft union. Differring from decreasing rapidly in the incompatible graft, the curves of IAA showed a peak at the 8th day after grafting when the vascular bridges formed in the compatible graft.