Plantlet regeneration and chromosome variation in tobacco (Nicotiana tabacum cv. Wisconsin 38) tumor clone transformed by Agrobacterium tumefaciens were investigated. Transformed calluses differentiated shoots on the hormone-free MS medium. The root was efficiently developed from shoot-cut within 2 weeks on the MS medium supplemented with 10 μM IAA and 0.1 μM kinetin. In root tip mitosis of regenerant from transformed cell lines, 34 plants derived from tumor clone transformed by A. tumefaciens C58 showed 48 chromosomes. In regenerants derived from that of A. tumefaciens B6, 45 plants showed 48 chromosomes, one tetraploid and one hypertetraploid of its chromosome number about 101.