This study was conducted to fi nd out an effective concentration of colchicine for inducing polyploidy in Impatiens patula Craib. The colchicine concentrations used in the experiment were 0, 0.03, 0.05 and 0.09% with the incubation period of three hours. All colchicine treated shoot tips were cultured on MS medium without growth regulator for six weeks. It was found that increasing doses of colchicine resulted in decreasing of the average shoot length, the number of node, leaf and flower and also the percentage of in vitro flowering. However, colchicine concentrations used in this experiment had no effect on the size of flower. Colchicine concentration at 0.05% led to tetraploid induction and provided the highest average thickness of leaf (309 μm) and largest size of stomata (68.8 μm). The tetraploid plantlets gave the higher chloroplast number than those of diploid plantlets.