Mung bean ( Phaseolus radiatus ) was used as subject in this study exploring responses of root border cells to cadmium toxicity in vitro and in vivo with the methods of pre-suspended culture using agar pour plate and filter paper pad in the later part of the culture. In the experiment mung bean root tips with root border cells unwashed in group A and washed off in group B were treated with different concentrations of Cd²⁺. Results show that Cd²⁺ induced apoptosis and then mucus secretion of the root border cells in vitro. Survival rate of the root border cells in vitro decreased with increasing concentration of Cd²⁺. It was also found that Cd²⁺ induced in vivo generation of root border cells, of which the number increased first and then decreased with the increasing Cd²⁺ concentration. The maximum induction effect was observed when the roots were treated with 50μmolL^-1 Cd²⁺, regardless of whether the root border cells were washed off or not; Cd²⁺ affected survival rate of the root border cells, and in Group A, the survival rate of root border cells decreased gradually with the increasing Cd²⁺ concentration, but in Group B it increased first and decreased later. Compared with the control, the treatments of 25μmolL^-1，200μmolL^-1and 400μmolL^-1 varied significantly (p< 0.05 ), PME activity of root cap increased with increasing Cd²⁺ concentration, and the effect was significant（p<0.05）when the roots were treated with a high concentration of Cd²⁺concentration for 24h. All the above-described findings indicate that mung bean root tips can release more root border cells under Cd²⁺ stress, and the detached root border cells form a layer of mucilage and apoptotic cells to protect the root tips against Cd²⁺ .