Abstract: 【Objective】The study was conducted in order to investigate the changes in physiological and biochemical characters of sweet potato explants infected by Agrobacterium tumefaciens strain N9-1. 【Method】The stem, lamina and petiole explants of sweet potato cv. “Xindazi” infected by A. tumefaciens strain N9-1 were taken after 0, 1, 3, 5 days of cocultivation respectively and investigate the changes in physiological and biochemical characters. 【Results】The changes in the contents of soluble protein in stem, lamina and petiole explants infected by A. tumefaciens were showed a tendency to decrease gradually since the increasing of co-culture time. During the primary period of infection, a lot of POD and SOD in the explants would be used up due to occurrence of the stress. So the activities of POD and SOD would decrease at this period. In the later stage of infection, the reason why the activities of POD and SOD would increase may be that the mechanism of disease resistance in plant had functioned. The change tendencies in contents of endogenous hormones ABA and GA3 in the infected stem, petiole and lamina explants were showed increasing first and then decreasing, while the contents of iPAs in them showed a tendency on the contrary. During the suitable co-culture time of the stem explants (about 3 days), the activities of POD increased gently, while the activities of SOD, the contents of endogenous hormones GA3 and iPAs were in the relatively lower range, and the content of ABA were in the higher range. 【Conclusion】During the period of infection, the contents of soluble protein, the activities of POD and SOD, the contents of endogenous hormones in explants infected by A. tumefaciens were changed due to occurrence of the stress. All of these change tendencies in explants infected by A. tumefaciens were similar to those in plants infected by other bacterium in field.