Abstract: Explants of Anoectochilus roxburghii were adopted and treated with 300 mg·L_-1 colchicine for doubling the chromosome number. As the treating time being prolonged, the toxic effect of colchicine became more evident because the death rate of explants increased. Tetraploid cells were induced from the experiments when the explants were treated with colchicine at this level for 3-19 days. The best chromosome doubling results of 72.7% tetraploid cell frequency and 91% induction rate were obtained when explants were treated for 13 days. The number of chromosome of diploids and tetraploids were 40 and 80, respectively. The stoma size of tetraploids was larger than that of diploids. No difference was found between the stoma size of diploids and mix-ploids．

Key words: Anoectochilus roxburghii, in vitro culture, polyploidy, colchicine