To screen a suitable method for inducing tetraploid with high frequency, five diploid inbred lines of watermelon, WC-8C-2C, WD-2-6K, GW11, GW7, and GW2 were selected. The efficiency of chromosome doubling with three methods direct seed (DS), shoot apex (SA), and inverted hypocotyl (IH) were tested by applying two different concentrations (0.1% and 0.2%) of antimitotic agent, colchicine, during the period January, 2010 to August, 2011 at Watermelon Experiment Station, Daesan, Gochang, Jeonbuk, South Korea. Mean chloroplast counts were 12 and 19 in diploid and tetraploid, respectively. The highest rate of efficiency of generating tetraploids (29.5%) was recorded in 0.2% IH method and considered as s best method. A total of 71 new tetraploids were generated successfully using present methods and techniques. WC-8C-2C and GW7 produced maximum number of tetraploids.