Abstract:Some oncogenic Agrobacterium strains have positive reaction of 3-ketola-ctate on DYL medium and good growth ability in YBS medium with sucrose as carbon source. Other oncogenic Agrobacterium strains have negatiye reac- tion of 3-ketolactate reaction and bad growth ability in YBS medium. Using this relation, an oncogenic Agrobacterium strain K-8 was isolated from fresh and young crown gall of peach tree with media DYL and YBS. Four oncoge- nic strains isolated from China had been determined. The strain S-1 and strain B-1 are strains of Agrobacterium tumefaciens Biotype I. The strain K-8 and strain 702 are strains of Agrobacterium tumefaciens Biotype II.