Induction and culture of hairy roots by Agrobacterium rhizogenes A4 were carried out in Platycodon grandiflorum DC. After 2-4 weeks of inoculation with Agrobacterium rhizogenes hairy roots were formed at root segments in the balloon flower. Optimized growth of hairy roots was obtained in hormone-free MS medium, 6% sucrose and pH 5.8. The pattern of ginsenoside in the transformed roots was not different with that in the ordinary roots.